The Tor Browser: toolkit/components/aboutmemory/content/aboutMemory.js@b8a032363ba2 (annotated)

toolkit/components/aboutmemory/content/aboutMemory.js@b8a032363ba2 (annotated)

toolkit/components/aboutmemory/content/aboutMemory.js

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- Mode: js2; tab-width: 8; indent-tabs-mode: nil; js2-basic-offset: 2 -*-*/
 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 // You can direct about:memory to immediately load memory reports from a file
 // by providing a file= query string.  For example,
 //
 //     about:memory?file=/home/username/reports.json.gz
 //
 // "file=" is not case-sensitive.  We'll URI-unescape the contents of the
 // "file=" argument, and obviously the filename is case-sensitive iff you're on
 // a case-sensitive filesystem.  If you specify more than one "file=" argument,
 // only the first one is used.
 "use strict";
 //---------------------------------------------------------------------------
 const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cu = Components.utils;
 const CC = Components.Constructor;
 const KIND_NONHEAP           = Ci.nsIMemoryReporter.KIND_NONHEAP;
 const KIND_HEAP              = Ci.nsIMemoryReporter.KIND_HEAP;
 const KIND_OTHER             = Ci.nsIMemoryReporter.KIND_OTHER;
 const UNITS_BYTES            = Ci.nsIMemoryReporter.UNITS_BYTES;
 const UNITS_COUNT            = Ci.nsIMemoryReporter.UNITS_COUNT;
 const UNITS_COUNT_CUMULATIVE = Ci.nsIMemoryReporter.UNITS_COUNT_CUMULATIVE;
 const UNITS_PERCENTAGE       = Ci.nsIMemoryReporter.UNITS_PERCENTAGE;
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 XPCOMUtils.defineLazyGetter(this, "nsBinaryStream",
                             () => CC("@mozilla.org/binaryinputstream;1",
                                      "nsIBinaryInputStream",
                                      "setInputStream"));
 XPCOMUtils.defineLazyGetter(this, "nsFile",
                             () => CC("@mozilla.org/file/local;1",
                                      "nsIFile", "initWithPath"));
 XPCOMUtils.defineLazyGetter(this, "nsGzipConverter",
                             () => CC("@mozilla.org/streamconv;1?from=gzip&to=uncompressed",
                                      "nsIStreamConverter"));
 let gMgr = Cc["@mozilla.org/memory-reporter-manager;1"]
              .getService(Ci.nsIMemoryReporterManager);
 let gUnnamedProcessStr = "Main Process";
 let gIsDiff = false;
 //---------------------------------------------------------------------------
 // Forward slashes in URLs in paths are represented with backslashes to avoid
 // being mistaken for path separators.  Paths/names where this hasn't been
 // undone are prefixed with "unsafe"; the rest are prefixed with "safe".
 function flipBackslashes(aUnsafeStr)
 {
   // Save memory by only doing the replacement if it's necessary.
   return (aUnsafeStr.indexOf('\\') === -1)
          ? aUnsafeStr
          : aUnsafeStr.replace(/\\/g, '/');
 }
 const gAssertionFailureMsgPrefix = "aboutMemory.js assertion failed: ";
 // This is used for things that should never fail, and indicate a defect in
 // this file if they do.
 function assert(aCond, aMsg)
 {
   if (!aCond) {
     reportAssertionFailure(aMsg)
     throw(gAssertionFailureMsgPrefix + aMsg);
   }
 }
 // This is used for malformed input from memory reporters.
 function assertInput(aCond, aMsg)
 {
   if (!aCond) {
     throw "Invalid memory report(s): " + aMsg;
   }
 }
 function handleException(ex)
 {
   let str = ex.toString();
   if (str.startsWith(gAssertionFailureMsgPrefix)) {
     // Argh, assertion failure within this file!  Give up.
     throw ex;
   } else {
     // File or memory reporter problem.  Print a message.
     updateMainAndFooter(ex.toString(), HIDE_FOOTER, "badInputWarning");
   }
 }
 function reportAssertionFailure(aMsg)
 {
   let debug = Cc["@mozilla.org/xpcom/debug;1"].getService(Ci.nsIDebug2);
   if (debug.isDebugBuild) {
     debug.assertion(aMsg, "false", "aboutMemory.js", 0);
   }
 }
 function debug(x)
 {
   let section = appendElement(document.body, 'div', 'section');
   appendElementWithText(section, "div", "debug", JSON.stringify(x));
 }
 //---------------------------------------------------------------------------
 function onUnload()
 {
 }
 //---------------------------------------------------------------------------
 // The <div> holding everything but the header and footer (if they're present).
 // It's what is updated each time the page changes.
 let gMain;
 // The <div> holding the footer.
 let gFooter;
 // The "verbose" checkbox.
 let gVerbose;
 // Values for the second argument to updateMainAndFooter.
 let HIDE_FOOTER = 0;
 let SHOW_FOOTER = 1;
 function updateMainAndFooter(aMsg, aFooterAction, aClassName)
 {
   // Clear gMain by replacing it with an empty node.
   let tmp = gMain.cloneNode(false);
   gMain.parentNode.replaceChild(tmp, gMain);
   gMain = tmp;
   gMain.classList.remove('hidden');
   gMain.classList.remove('verbose');
   gMain.classList.remove('non-verbose');
   if (gVerbose) {
     gMain.classList.add(gVerbose.checked ? 'verbose' : 'non-verbose');
   }
   if (aMsg) {
     let className = "section"
     if (aClassName) {
       className = className + " " + aClassName;
     }
     appendElementWithText(gMain, 'div', className, aMsg);
   }
   switch (aFooterAction) {
    case HIDE_FOOTER:   gFooter.classList.add('hidden');    break;
    case SHOW_FOOTER:   gFooter.classList.remove('hidden'); break;
    default: assertInput(false, "bad footer action in updateMainAndFooter");
   }
 }
 function appendTextNode(aP, aText)
 {
   let e = document.createTextNode(aText);
   aP.appendChild(e);
   return e;
 }
 function appendElement(aP, aTagName, aClassName)
 {
   let e = document.createElement(aTagName);
   if (aClassName) {
     e.className = aClassName;
   }
   aP.appendChild(e);
   return e;
 }
 function appendElementWithText(aP, aTagName, aClassName, aText)
 {
   let e = appendElement(aP, aTagName, aClassName);
   // Setting textContent clobbers existing children, but there are none.  More
   // importantly, it avoids creating a JS-land object for the node, saving
   // memory.
   e.textContent = aText;
   return e;
 }
 //---------------------------------------------------------------------------
 const explicitTreeDescription =
 "This tree covers explicit memory allocations by the application.  It includes \
 \n\n\
 * allocations made at the operating system level (via calls to functions such as \
 VirtualAlloc, vm_allocate, and mmap), \
 \n\n\
 * allocations made at the heap allocation level (via functions such as malloc, \
 calloc, realloc, memalign, operator new, and operator new[]) that have not been \
 explicitly decommitted (i.e. evicted from memory and swap), and \
 \n\n\
 * where possible, the overhead of the heap allocator itself.\
 \n\n\
 It excludes memory that is mapped implicitly such as code and data segments, \
 and thread stacks. \
 \n\n\
 'explicit' is not guaranteed to cover every explicit allocation, but it does cover \
 most (including the entire heap), and therefore it is the single best number to \
 focus on when trying to reduce memory usage.";
 //---------------------------------------------------------------------------
 function appendButton(aP, aTitle, aOnClick, aText, aId)
 {
   let b = appendElementWithText(aP, "button", "", aText);
   b.title = aTitle;
   b.onclick = aOnClick;
   if (aId) {
     b.id = aId;
   }
   return b;
 }
 function appendHiddenFileInput(aP, aId, aChangeListener)
 {
   let input = appendElementWithText(aP, "input", "hidden", "");
   input.type = "file";
   input.id = aId;      // used in testing
   input.addEventListener("change", aChangeListener);
   return input;
 }
 function onLoad()
 {
   // Generate the header.
   let header = appendElement(document.body, "div", "ancillary");
   // A hidden file input element that can be invoked when necessary.
   let fileInput1 = appendHiddenFileInput(header, "fileInput1", function() {
     let file = this.files[0];
     let filename = file.mozFullPath;
     updateAboutMemoryFromFile(filename);
   });
   // Ditto.
   let fileInput2 =
       appendHiddenFileInput(header, "fileInput2", function(e) {
     let file = this.files[0];
     // First time around, we stash a copy of the filename and reinvoke.  Second
     // time around we do the diff and display.
     if (!this.filename1) {
       this.filename1 = file.mozFullPath;
       // e.skipClick is only true when testing -- it allows fileInput2's
       // onchange handler to be re-called without having to go via the file
       // picker.
       if (!e.skipClick) {
         this.click();
       }
     } else {
       let filename1 = this.filename1;
       delete this.filename1;
       updateAboutMemoryFromTwoFiles(filename1, file.mozFullPath);
     }
   });
   const CuDesc = "Measure current memory reports and show.";
   const LdDesc = "Load memory reports from file and show.";
   const DfDesc = "Load memory report data from two files and show the " +
                  "difference.";
   const RdDesc = "Read memory reports from the clipboard and show.";
   const SvDesc = "Save memory reports to file.";
   const GCDesc = "Do a global garbage collection.";
   const CCDesc = "Do a cycle collection.";
   const MMDesc = "Send three \"heap-minimize\" notifications in a " +
                  "row.  Each notification triggers a global garbage " +
                  "collection followed by a cycle collection, and causes the " +
                  "process to reduce memory usage in other ways, e.g. by " +
                  "flushing various caches.";
   const GCAndCCLogDesc = "Save garbage collection log and concise cycle " +
                          "collection log.\n" +
                          "WARNING: These logs may be large (>1GB).";
   const GCAndCCAllLogDesc = "Save garbage collection log and verbose cycle " +
                             "collection log.\n" +
                             "WARNING: These logs may be large (>1GB).";
   let ops = appendElement(header, "div", "");
   let row1 = appendElement(ops, "div", "opsRow");
   let labelDiv =
    appendElementWithText(row1, "div", "opsRowLabel", "Show memory reports");
   let label = appendElementWithText(labelDiv, "label", "");
   gVerbose = appendElement(label, "input", "");
   gVerbose.type = "checkbox";
   gVerbose.id = "verbose";   // used for testing
   appendTextNode(label, "verbose");
   const kEllipsis = "\u2026";
   // The "measureButton" id is used for testing.
   appendButton(row1, CuDesc, doMeasure, "Measure", "measureButton");
   appendButton(row1, LdDesc, () => fileInput1.click(), "Load" + kEllipsis);
   appendButton(row1, DfDesc, () => fileInput2.click(),
                "Load and diff" + kEllipsis);
   appendButton(row1, RdDesc, updateAboutMemoryFromClipboard,
                "Read from clipboard");
   let row2 = appendElement(ops, "div", "opsRow");
   appendElementWithText(row2, "div", "opsRowLabel", "Save memory reports");
   appendButton(row2, SvDesc, saveReportsToFile, "Measure and save" + kEllipsis);
   let row3 = appendElement(ops, "div", "opsRow");
   appendElementWithText(row3, "div", "opsRowLabel", "Free memory");
   appendButton(row3, GCDesc, doGC,  "GC");
   appendButton(row3, CCDesc, doCC,  "CC");
   appendButton(row3, MMDesc, doMMU, "Minimize memory usage");
   let row4 = appendElement(ops, "div", "opsRow");
   appendElementWithText(row4, "div", "opsRowLabel", "Save GC & CC logs");
   appendButton(row4, GCAndCCLogDesc,
                saveGCLogAndConciseCCLog, "Save concise", 'saveLogsConcise');
   appendButton(row4, GCAndCCAllLogDesc,
                saveGCLogAndVerboseCCLog, "Save verbose", 'saveLogsVerbose');
   // Generate the main div, where content ("section" divs) will go.  It's
   // hidden at first.
   gMain = appendElement(document.body, 'div', '');
   gMain.id = 'mainDiv';
   // Generate the footer.  It's hidden at first.
   gFooter = appendElement(document.body, 'div', 'ancillary hidden');
   let a = appendElementWithText(gFooter, "a", "option",
                                 "Troubleshooting information");
   a.href = "about:support";
   let legendText1 = "Click on a non-leaf node in a tree to expand ('++') " +
                     "or collapse ('--') its children.";
   let legendText2 = "Hover the pointer over the name of a memory report " +
                     "to see a description of what it measures.";
   appendElementWithText(gFooter, "div", "legend", legendText1);
   appendElementWithText(gFooter, "div", "legend hiddenOnMobile", legendText2);
   // See if we're loading from a file.  (Because about:memory is a non-standard
   // URL, location.search is undefined, so we have to use location.href
   // instead.)
   let search = location.href.split('?')[1];
   if (search) {
     let searchSplit = search.split('&');
     for (let i = 0; i < searchSplit.length; i++) {
       if (searchSplit[i].toLowerCase().startsWith('file=')) {
         let filename = searchSplit[i].substring('file='.length);
         updateAboutMemoryFromFile(decodeURIComponent(filename));
         return;
       }
     }
   }
 }
 //---------------------------------------------------------------------------
 function doGC()
 {
   Services.obs.notifyObservers(null, "child-gc-request", null);
   Cu.forceGC();
   updateMainAndFooter("Garbage collection completed", HIDE_FOOTER);
 }
 function doCC()
 {
   Services.obs.notifyObservers(null, "child-cc-request", null);
   window.QueryInterface(Ci.nsIInterfaceRequestor)
         .getInterface(Ci.nsIDOMWindowUtils)
         .cycleCollect();
   updateMainAndFooter("Cycle collection completed", HIDE_FOOTER);
 }
 function doMMU()
 {
   Services.obs.notifyObservers(null, "child-mmu-request", null);
   gMgr.minimizeMemoryUsage(
     () => updateMainAndFooter("Memory minimization completed", HIDE_FOOTER));
 }
 function doMeasure()
 {
   updateAboutMemoryFromReporters();
 }
 function saveGCLogAndConciseCCLog()
 {
   dumpGCLogAndCCLog(false);
 }
 function saveGCLogAndVerboseCCLog()
 {
   dumpGCLogAndCCLog(true);
 }
 function dumpGCLogAndCCLog(aVerbose)
 {
   let gcLogPath = {};
   let ccLogPath = {};
   let dumper = Cc["@mozilla.org/memory-info-dumper;1"]
                 .getService(Ci.nsIMemoryInfoDumper);
   updateMainAndFooter("Saving logs...", HIDE_FOOTER);
   dumper.dumpGCAndCCLogsToFile("", aVerbose, /* dumpChildProcesses = */ false,
                                gcLogPath, ccLogPath);
   updateMainAndFooter("", HIDE_FOOTER);
   let section = appendElement(gMain, 'div', "section");
   appendElementWithText(section, 'div', "",
                         "Saved GC log to " + gcLogPath.value);
   let ccLogType = aVerbose ? "verbose" : "concise";
   appendElementWithText(section, 'div', "",
                         "Saved " + ccLogType + " CC log to " + ccLogPath.value);
 }
 /**
  * Top-level function that does the work of generating the page from the memory
  * reporters.
  */
 function updateAboutMemoryFromReporters()
 {
   updateMainAndFooter("Measuring...", HIDE_FOOTER);
   try {
     let processLiveMemoryReports =
         function(aHandleReport, aDisplayReports) {
       let handleReport = function(aProcess, aUnsafePath, aKind, aUnits,
                                   aAmount, aDescription) {
         aHandleReport(aProcess, aUnsafePath, aKind, aUnits, aAmount,
                       aDescription, /* presence = */ undefined);
       }
       let displayReportsAndFooter = function() {
         updateMainAndFooter("", SHOW_FOOTER);
         aDisplayReports();
       }
       gMgr.getReports(handleReport, null,
                       displayReportsAndFooter, null);
     }
     // Process the reports from the live memory reporters.
     appendAboutMemoryMain(processLiveMemoryReports,
                           gMgr.hasMozMallocUsableSize);
   } catch (ex) {
     handleException(ex);
   }
 }
 // Increment this if the JSON format changes.
 //
 var gCurrentFileFormatVersion = 1;
 /**
  * Populate about:memory using the data in the given JSON object.
  *
  * @param aObj
  *        An object containing JSON data that (hopefully!) conforms to the
  *        schema used by nsIMemoryInfoDumper.
  */
 function updateAboutMemoryFromJSONObject(aObj)
 {
   try {
     assertInput(aObj.version === gCurrentFileFormatVersion,
                 "data version number missing or doesn't match");
     assertInput(aObj.hasMozMallocUsableSize !== undefined,
                 "missing 'hasMozMallocUsableSize' property");
     assertInput(aObj.reports && aObj.reports instanceof Array,
                 "missing or non-array 'reports' property");
     let processMemoryReportsFromFile =
         function(aHandleReport, aDisplayReports) {
       for (let i = 0; i < aObj.reports.length; i++) {
         let r = aObj.reports[i];
         // A hack: for a brief time (late in the FF26 and early in the FF27
         // cycle) we were dumping memory report files that contained reports
         // whose path began with "redundant/".  Such reports were ignored by
         // about:memory.  These reports are no longer produced, but some older
         // builds are still floating around and producing files that contain
         // them, so we need to still handle them (i.e. ignore them).  This hack
         // can be removed once FF26 and associated products (e.g. B2G 1.2) are
         // no longer in common use.
         if (!r.path.startsWith("redundant/")) {
           aHandleReport(r.process, r.path, r.kind, r.units, r.amount,
                         r.description, r._presence);
         }
       }
       aDisplayReports();
     }
     appendAboutMemoryMain(processMemoryReportsFromFile,
                           aObj.hasMozMallocUsableSize);
   } catch (ex) {
     handleException(ex);
   }
 }
 /**
  * Populate about:memory using the data in the given JSON string.
  *
  * @param aStr
  *        A string containing JSON data conforming to the schema used by
  *        nsIMemoryReporterManager::dumpReports.
  */
 function updateAboutMemoryFromJSONString(aStr)
 {
   try {
     let obj = JSON.parse(aStr);
     updateAboutMemoryFromJSONObject(obj);
   } catch (ex) {
     handleException(ex);
   }
 }
 /**
  * Loads the contents of a file into a string and passes that to a callback.
  *
  * @param aFilename
  *        The name of the file being read from.
  * @param aFn
  *        The function to call and pass the read string to upon completion.
  */
 function loadMemoryReportsFromFile(aFilename, aFn)
 {
   updateMainAndFooter("Loading...", HIDE_FOOTER);
   try {
     let reader = new FileReader();
     reader.onerror = () => { throw "FileReader.onerror"; };
     reader.onabort = () => { throw "FileReader.onabort"; };
     reader.onload = (aEvent) => {
       updateMainAndFooter("", SHOW_FOOTER);  // Clear "Loading..." from above.
       aFn(aEvent.target.result);
     };
     // If it doesn't have a .gz suffix, read it as a (legacy) ungzipped file.
     if (!aFilename.endsWith(".gz")) {
       reader.readAsText(new File(aFilename));
       return;
     }
     // Read compressed gzip file.
     let converter = new nsGzipConverter();
     converter.asyncConvertData("gzip", "uncompressed", {
       data: [],
       onStartRequest: function(aR, aC) {},
       onDataAvailable: function(aR, aC, aStream, aO, aCount) {
         let bi = new nsBinaryStream(aStream);
         this.data.push(bi.readBytes(aCount));
       },
       onStopRequest: function(aR, aC, aStatusCode) {
         try {
           if (!Components.isSuccessCode(aStatusCode)) {
             throw aStatusCode;
           }
           reader.readAsText(new Blob(this.data));
         } catch (ex) {
           handleException(ex);
         }
       }
     }, null);
     let file = new nsFile(aFilename);
     let fileChan = Services.io.newChannelFromURI(Services.io.newFileURI(file));
     fileChan.asyncOpen(converter, null);
   } catch (ex) {
     handleException(ex);
   }
 }
 /**
  * Like updateAboutMemoryFromReporters(), but gets its data from a file instead
  * of the memory reporters.
  *
  * @param aFilename
  *        The name of the file being read from.  The expected format of the
  *        file's contents is described in a comment in nsIMemoryInfoDumper.idl.
  */
 function updateAboutMemoryFromFile(aFilename)
 {
   loadMemoryReportsFromFile(aFilename,
                             updateAboutMemoryFromJSONString);
 }
 /**
  * Like updateAboutMemoryFromFile(), but gets its data from a two files and
  * diffs them.
  *
  * @param aFilename1
  *        The name of the first file being read from.
  * @param aFilename2
  *        The name of the first file being read from.
  */
 function updateAboutMemoryFromTwoFiles(aFilename1, aFilename2)
 {
   loadMemoryReportsFromFile(aFilename1, function(aStr1) {
     loadMemoryReportsFromFile(aFilename2, function f2(aStr2) {
       try {
         let obj1 = JSON.parse(aStr1);
         let obj2 = JSON.parse(aStr2);
         gIsDiff = true;
         updateAboutMemoryFromJSONObject(diffJSONObjects(obj1, obj2));
         gIsDiff = false;
       } catch (ex) {
         handleException(ex);
       }
     });
   });
 }
 /**
  * Like updateAboutMemoryFromFile(), but gets its data from the clipboard
  * instead of a file.
  */
 function updateAboutMemoryFromClipboard()
 {
   // Get the clipboard's contents.
   let transferable = Cc["@mozilla.org/widget/transferable;1"]
                        .createInstance(Ci.nsITransferable);
   let loadContext = window.QueryInterface(Ci.nsIInterfaceRequestor)
                           .getInterface(Ci.nsIWebNavigation)
                           .QueryInterface(Ci.nsILoadContext);
   transferable.init(loadContext);
   transferable.addDataFlavor('text/unicode');
   Services.clipboard.getData(transferable, Ci.nsIClipboard.kGlobalClipboard);
   var cbData = {};
   try {
     transferable.getTransferData('text/unicode', cbData,
                                  /* out dataLen (ignored) */ {});
     let cbString = cbData.value.QueryInterface(Ci.nsISupportsString).data;
     // Success!  Now use the string to generate about:memory.
     updateAboutMemoryFromJSONString(cbString);
   } catch (ex) {
     handleException(ex);
   }
 }
 //---------------------------------------------------------------------------
 // Something unlikely to appear in a process name.
 let kProcessPathSep = "^:^:^";
 // Short for "diff report".
 function DReport(aKind, aUnits, aAmount, aDescription, aNMerged, aPresence)
 {
   this._kind = aKind;
   this._units = aUnits;
   this._amount = aAmount;
   this._description = aDescription;
   this._nMerged = aNMerged;
   if (aPresence !== undefined) {
     this._presence = aPresence;
   }
 }
 DReport.prototype = {
   assertCompatible: function(aKind, aUnits)
   {
     assert(this._kind  == aKind,  "Mismatched kinds");
     assert(this._units == aUnits, "Mismatched units");
     // We don't check that the "description" properties match.  This is because
     // on Linux we can get cases where the paths are the same but the
     // descriptions differ, like this:
     //
     //   "path": "size/other-files/icon-theme.cache/[r--p]",
     //   "description": "/usr/share/icons/gnome/icon-theme.cache (read-only, not executable, private)"
     //
     //   "path": "size/other-files/icon-theme.cache/[r--p]"
     //   "description": "/usr/share/icons/hicolor/icon-theme.cache (read-only, not executable, private)"
     //
     // In those cases, we just use the description from the first-encountered
     // one, which is what about:memory also does.
     // (Note: reports with those paths are no longer generated, but allowing
     // the descriptions to differ seems reasonable.)
   },
   merge: function(aJr) {
     this.assertCompatible(aJr.kind, aJr.units);
     this._amount += aJr.amount;
     this._nMerged++;
   },
   toJSON: function(aProcess, aPath, aAmount) {
     return {
       process:     aProcess,
       path:        aPath,
       kind:        this._kind,
       units:       this._units,
       amount:      aAmount,
       description: this._description,
       _presence:   this._presence
     };
   }
 };
 // Constants that indicate if a DReport was present only in one of the data
 // sets, or had to be added for balance.
 DReport.PRESENT_IN_FIRST_ONLY  = 1;
 DReport.PRESENT_IN_SECOND_ONLY = 2;
 DReport.ADDED_FOR_BALANCE = 3;
 /**
  * Make a report map, which has combined path+process strings for keys, and
  * DReport objects for values.
  *
  * @param aJSONReports
  *        The |reports| field of a JSON object.
  * @return The constructed report map.
  */
 function makeDReportMap(aJSONReports)
 {
   let dreportMap = {};
   for (let i = 0; i < aJSONReports.length; i++) {
     let jr = aJSONReports[i];
     assert(jr.process     !== undefined, "Missing process");
     assert(jr.path        !== undefined, "Missing path");
     assert(jr.kind        !== undefined, "Missing kind");
     assert(jr.units       !== undefined, "Missing units");
     assert(jr.amount      !== undefined, "Missing amount");
     assert(jr.description !== undefined, "Missing description");
     // Strip out some non-deterministic stuff that prevents clean diffs --
     // e.g. PIDs, addresses.
     let strippedProcess = jr.process.replace(/pid \d+/, "pid NNN");
     let strippedPath = jr.path.replace(/0x[0-9A-Fa-f]+/, "0xNNN");
     let processPath = strippedProcess + kProcessPathSep + strippedPath;
     let rOld = dreportMap[processPath];
     if (rOld === undefined) {
       dreportMap[processPath] =
         new DReport(jr.kind, jr.units, jr.amount, jr.description, 1, undefined);
     } else {
       rOld.merge(jr);
     }
   }
   return dreportMap;
 }
 // Return a new dreportMap which is the diff of two dreportMaps.  Empties
 // aDReportMap2 along the way.
 function diffDReportMaps(aDReportMap1, aDReportMap2)
 {
   let result = {};
   for (let processPath in aDReportMap1) {
     let r1 = aDReportMap1[processPath];
     let r2 = aDReportMap2[processPath];
     let r2_amount, r2_nMerged;
     let presence;
     if (r2 !== undefined) {
       r1.assertCompatible(r2._kind, r2._units);
       r2_amount = r2._amount;
       r2_nMerged = r2._nMerged;
       delete aDReportMap2[processPath];
       presence = undefined;   // represents that it's present in both
     } else {
       r2_amount = 0;
       r2_nMerged = 0;
       presence = DReport.PRESENT_IN_FIRST_ONLY;
     }
     result[processPath] =
       new DReport(r1._kind, r1._units, r2_amount - r1._amount, r1._description,
                   Math.max(r1._nMerged, r2_nMerged), presence);
   }
   for (let processPath in aDReportMap2) {
     let r2 = aDReportMap2[processPath];
     result[processPath] = new DReport(r2._kind, r2._units, r2._amount,
                                       r2._description, r2._nMerged,
                                       DReport.PRESENT_IN_SECOND_ONLY);
   }
   return result;
 }
 function makeJSONReports(aDReportMap)
 {
   let reports = [];
   for (let processPath in aDReportMap) {
     let r = aDReportMap[processPath];
     if (r._amount !== 0) {
       // If _nMerged > 1, we give the full (aggregated) amount in the first
       // copy, and then use amount=0 in the remainder.  When viewed in
       // about:memory, this shows up as an entry with a "[2]"-style suffix
       // and the correct amount.
       let split = processPath.split(kProcessPathSep);
       assert(split.length >= 2);
       let process = split.shift();
       let path = split.join();
       reports.push(r.toJSON(process, path, r._amount));
       for (let i = 1; i < r._nMerged; i++) {
         reports.push(r.toJSON(process, path, 0));
       }
     }
   }
   return reports;
 }
 // Diff two JSON objects holding memory reports.
 function diffJSONObjects(aJson1, aJson2)
 {
   function simpleProp(aProp)
   {
     assert(aJson1[aProp] !== undefined && aJson1[aProp] === aJson2[aProp],
            aProp + " properties don't match");
     return aJson1[aProp];
   }
   return {
     version: simpleProp("version"),
     hasMozMallocUsableSize: simpleProp("hasMozMallocUsableSize"),
     reports: makeJSONReports(diffDReportMaps(makeDReportMap(aJson1.reports),
                                              makeDReportMap(aJson2.reports)))
   };
 }
 //---------------------------------------------------------------------------
 // |PColl| is short for "process collection".
 function PColl()
 {
   this._trees = {};
   this._degenerates = {};
   this._heapTotal = 0;
 }
 /**
  * Processes reports (whether from reporters or from a file) and append the
  * main part of the page.
  *
  * @param aProcessReports
  *        Function that extracts the memory reports from the reporters or from
  *        file.
  * @param aHasMozMallocUsableSize
  *        Boolean indicating if moz_malloc_usable_size works.
  */
 function appendAboutMemoryMain(aProcessReports, aHasMozMallocUsableSize)
 {
   let pcollsByProcess = {};
   function handleReport(aProcess, aUnsafePath, aKind, aUnits, aAmount,
                         aDescription, aPresence)
   {
     if (aUnsafePath.startsWith("explicit/")) {
       assertInput(aKind === KIND_HEAP || aKind === KIND_NONHEAP,
                   "bad explicit kind");
       assertInput(aUnits === UNITS_BYTES, "bad explicit units");
     }
     assert(aPresence === undefined ||
            aPresence == DReport.PRESENT_IN_FIRST_ONLY ||
            aPresence == DReport.PRESENT_IN_SECOND_ONLY,
            "bad presence");
     let process = aProcess === "" ? gUnnamedProcessStr : aProcess;
     let unsafeNames = aUnsafePath.split('/');
     let unsafeName0 = unsafeNames[0];
     let isDegenerate = unsafeNames.length === 1;
     // Get the PColl table for the process, creating it if necessary.
     let pcoll = pcollsByProcess[process];
     if (!pcollsByProcess[process]) {
       pcoll = pcollsByProcess[process] = new PColl();
     }
     // Get the root node, creating it if necessary.
     let psubcoll = isDegenerate ? pcoll._degenerates : pcoll._trees;
     let t = psubcoll[unsafeName0];
     if (!t) {
       t = psubcoll[unsafeName0] =
         new TreeNode(unsafeName0, aUnits, isDegenerate);
     }
     if (!isDegenerate) {
       // Add any missing nodes in the tree implied by aUnsafePath, and fill in
       // the properties that we can with a top-down traversal.
       for (let i = 1; i < unsafeNames.length; i++) {
         let unsafeName = unsafeNames[i];
         let u = t.findKid(unsafeName);
         if (!u) {
           u = new TreeNode(unsafeName, aUnits, isDegenerate);
           if (!t._kids) {
             t._kids = [];
           }
           t._kids.push(u);
         }
         t = u;
       }
       // Update the heap total if necessary.
       if (unsafeName0 === "explicit" && aKind == KIND_HEAP) {
         pcollsByProcess[process]._heapTotal += aAmount;
       }
     }
     if (t._amount) {
       // Duplicate!  Sum the values and mark it as a dup.
       t._amount += aAmount;
       t._nMerged = t._nMerged ? t._nMerged + 1 : 2;
       assert(t._presence === aPresence, "presence mismatch");
     } else {
       // New leaf node.  Fill in extra node details from the report.
       t._amount = aAmount;
       t._description = aDescription;
       if (aPresence !== undefined) {
         t._presence = aPresence;
       }
     }
   }
   function displayReports()
   {
     // Sort the processes.
     let processes = Object.keys(pcollsByProcess);
     processes.sort(function(aProcessA, aProcessB) {
       assert(aProcessA != aProcessB,
              "Elements of Object.keys() should be unique, but " +
              "saw duplicate '" + aProcessA + "' elem.");
       // Always put the main process first.
       if (aProcessA == gUnnamedProcessStr) {
         return -1;
       }
       if (aProcessB == gUnnamedProcessStr) {
         return 1;
       }
       // Then sort by resident size.
       let nodeA = pcollsByProcess[aProcessA]._degenerates['resident'];
       let nodeB = pcollsByProcess[aProcessB]._degenerates['resident'];
       let residentA = nodeA ? nodeA._amount : -1;
       let residentB = nodeB ? nodeB._amount : -1;
       if (residentA > residentB) {
         return -1;
       }
       if (residentA < residentB) {
         return 1;
       }
       // Then sort by process name.
       if (aProcessA < aProcessB) {
         return -1;
       }
       if (aProcessA > aProcessB) {
         return 1;
       }
       return 0;
     });
     // Generate output for each process.
     for (let i = 0; i < processes.length; i++) {
       let process = processes[i];
       let section = appendElement(gMain, 'div', 'section');
       appendProcessAboutMemoryElements(section, i, process,
                                        pcollsByProcess[process]._trees,
                                        pcollsByProcess[process]._degenerates,
                                        pcollsByProcess[process]._heapTotal,
                                        aHasMozMallocUsableSize);
     }
   }
   aProcessReports(handleReport, displayReports);
 }
 //---------------------------------------------------------------------------
 // There are two kinds of TreeNode.
 // - Leaf TreeNodes correspond to reports.
 // - Non-leaf TreeNodes are just scaffolding nodes for the tree;  their values
 //   are derived from their children.
 // Some trees are "degenerate", i.e. they contain a single node, i.e. they
 // correspond to a report whose path has no '/' separators.
 function TreeNode(aUnsafeName, aUnits, aIsDegenerate)
 {
   this._units = aUnits;
   this._unsafeName = aUnsafeName;
   if (aIsDegenerate) {
     this._isDegenerate = true;
   }
   // Leaf TreeNodes have these properties added immediately after construction:
   // - _amount
   // - _description
   // - _nMerged (only defined if > 1)
   // - _presence (only defined if value is PRESENT_IN_{FIRST,SECOND}_ONLY)
   //
   // Non-leaf TreeNodes have these properties added later:
   // - _kids
   // - _amount
   // - _description
   // - _hideKids (only defined if true)
 }
 TreeNode.prototype = {
   findKid: function(aUnsafeName) {
     if (this._kids) {
       for (let i = 0; i < this._kids.length; i++) {
         if (this._kids[i]._unsafeName === aUnsafeName) {
           return this._kids[i];
         }
       }
     }
     return undefined;
   },
   toString: function() {
     switch (this._units) {
       case UNITS_BYTES:            return formatBytes(this._amount);
       case UNITS_COUNT:
       case UNITS_COUNT_CUMULATIVE: return formatInt(this._amount);
       case UNITS_PERCENTAGE:       return formatPercentage(this._amount);
       default:
         assertInput(false, "bad units in TreeNode.toString");
     }
   }
 };
 // Sort TreeNodes first by size, then by name.  This is particularly important
 // for the about:memory tests, which need a predictable ordering of reporters
 // which have the same amount.
 TreeNode.compareAmounts = function(aA, aB) {
   let a, b;
   if (gIsDiff) {
     a = Math.abs(aA._amount);
     b = Math.abs(aB._amount);
   } else {
     a = aA._amount;
     b = aB._amount;
   }
   if (a > b) {
     return -1;
   }
   if (a < b) {
     return 1;
   }
   return TreeNode.compareUnsafeNames(aA, aB);
 };
 TreeNode.compareUnsafeNames = function(aA, aB) {
   return aA._unsafeName < aB._unsafeName ? -1 :
          aA._unsafeName > aB._unsafeName ?  1 :
 ;
 };
 /**
  * Fill in the remaining properties for the specified tree in a bottom-up
  * fashion.
  *
  * @param aRoot
  *        The tree root.
  */
 function fillInTree(aRoot)
 {
   // Fill in the remaining properties bottom-up.
   function fillInNonLeafNodes(aT)
   {
     if (!aT._kids) {
       // Leaf node.  Has already been filled in.
     } else if (aT._kids.length === 1 && aT != aRoot) {
       // Non-root, non-leaf node with one child.  Merge the child with the node
       // to avoid redundant entries.
       let kid = aT._kids[0];
       let kidBytes = fillInNonLeafNodes(kid);
       aT._unsafeName += '/' + kid._unsafeName;
       if (kid._kids) {
         aT._kids = kid._kids;
       } else {
         delete aT._kids;
       }
       aT._amount = kid._amount;
       aT._description = kid._description;
       if (kid._nMerged !== undefined) {
         aT._nMerged = kid._nMerged
       }
       assert(!aT._hideKids && !kid._hideKids, "_hideKids set when merging");
     } else {
       // Non-leaf node with multiple children.  Derive its _amount and
       // _description entirely from its children...
       let kidsBytes = 0;
       for (let i = 0; i < aT._kids.length; i++) {
         kidsBytes += fillInNonLeafNodes(aT._kids[i]);
       }
       // ... except in one special case. When diffing two memory report sets,
       // if one set has a node with children and the other has the same node
       // but without children -- e.g. the first has "a/b/c" and "a/b/d", but
       // the second only has "a/b" -- we need to add a fake node "a/b/(fake)"
       // to the second to make the trees comparable. It's ugly, but it works.
       if (aT._amount !== undefined &&
           (aT._presence === DReport.PRESENT_IN_FIRST_ONLY ||
            aT._presence === DReport.PRESENT_IN_SECOND_ONLY)) {
         aT._amount += kidsBytes;
         let fake = new TreeNode('(fake child)', aT._units);
         fake._presence = DReport.ADDED_FOR_BALANCE;
         fake._amount = aT._amount - kidsBytes;
         aT._kids.push(fake);
         delete aT._presence;
       } else {
         assert(aT._amount === undefined,
                "_amount already set for non-leaf node")
         aT._amount = kidsBytes;
       }
       aT._description = "The sum of all entries below this one.";
     }
     return aT._amount;
   }
   // cannotMerge is set because don't want to merge into a tree's root node.
   fillInNonLeafNodes(aRoot);
 }
 /**
  * Compute the "heap-unclassified" value and insert it into the "explicit"
  * tree.
  *
  * @param aT
  *        The "explicit" tree.
  * @param aHeapAllocatedNode
  *        The "heap-allocated" tree node.
  * @param aHeapTotal
  *        The sum of all explicit HEAP reports for this process.
  * @return A boolean indicating if "heap-allocated" is known for the process.
  */
 function addHeapUnclassifiedNode(aT, aHeapAllocatedNode, aHeapTotal)
 {
   if (aHeapAllocatedNode === undefined)
     return false;
   assert(aHeapAllocatedNode._isDegenerate, "heap-allocated is not degenerate");
   let heapAllocatedBytes = aHeapAllocatedNode._amount;
   let heapUnclassifiedT = new TreeNode("heap-unclassified", UNITS_BYTES);
   heapUnclassifiedT._amount = heapAllocatedBytes - aHeapTotal;
   heapUnclassifiedT._description =
       "Memory not classified by a more specific report. This includes " +
       "slop bytes due to internal fragmentation in the heap allocator " +
       "(caused when the allocator rounds up request sizes).";
   aT._kids.push(heapUnclassifiedT);
   aT._amount += heapUnclassifiedT._amount;
   return true;
 }
 /**
  * Sort all kid nodes from largest to smallest, and insert aggregate nodes
  * where appropriate.
  *
  * @param aTotalBytes
  *        The size of the tree's root node.
  * @param aT
  *        The tree.
  */
 function sortTreeAndInsertAggregateNodes(aTotalBytes, aT)
 {
   const kSignificanceThresholdPerc = 1;
   function isInsignificant(aT)
   {
     return !gVerbose.checked &&
            (100 * aT._amount / aTotalBytes) < kSignificanceThresholdPerc;
   }
   if (!aT._kids) {
     return;
   }
   aT._kids.sort(TreeNode.compareAmounts);
   // If the first child is insignificant, they all are, and there's no point
   // creating an aggregate node that lacks siblings.  Just set the parent's
   // _hideKids property and process all children.
   if (isInsignificant(aT._kids[0])) {
     aT._hideKids = true;
     for (let i = 0; i < aT._kids.length; i++) {
       sortTreeAndInsertAggregateNodes(aTotalBytes, aT._kids[i]);
     }
     return;
   }
   // Look at all children except the last one.
   let i;
   for (i = 0; i < aT._kids.length - 1; i++) {
     if (isInsignificant(aT._kids[i])) {
       // This child is below the significance threshold.  If there are other
       // (smaller) children remaining, move them under an aggregate node.
       let i0 = i;
       let nAgg = aT._kids.length - i0;
       // Create an aggregate node.  Inherit units from the parent;  everything
       // in the tree should have the same units anyway (we test this later).
       let aggT = new TreeNode("(" + nAgg + " tiny)", aT._units);
       aggT._kids = [];
       let aggBytes = 0;
       for ( ; i < aT._kids.length; i++) {
         aggBytes += aT._kids[i]._amount;
         aggT._kids.push(aT._kids[i]);
       }
       aggT._hideKids = true;
       aggT._amount = aggBytes;
       aggT._description =
         nAgg + " sub-trees that are below the " + kSignificanceThresholdPerc +
         "% significance threshold.";
       aT._kids.splice(i0, nAgg, aggT);
       aT._kids.sort(TreeNode.compareAmounts);
       // Process the moved children.
       for (i = 0; i < aggT._kids.length; i++) {
         sortTreeAndInsertAggregateNodes(aTotalBytes, aggT._kids[i]);
       }
       return;
     }
     sortTreeAndInsertAggregateNodes(aTotalBytes, aT._kids[i]);
   }
   // The first n-1 children were significant.  Don't consider if the last child
   // is significant;  there's no point creating an aggregate node that only has
   // one child.  Just process it.
   sortTreeAndInsertAggregateNodes(aTotalBytes, aT._kids[i]);
 }
 // Global variable indicating if we've seen any invalid values for this
 // process;  it holds the unsafePaths of any such reports.  It is reset for
 // each new process.
 let gUnsafePathsWithInvalidValuesForThisProcess = [];
 function appendWarningElements(aP, aHasKnownHeapAllocated,
                                aHasMozMallocUsableSize)
 {
   if (!aHasKnownHeapAllocated && !aHasMozMallocUsableSize) {
     appendElementWithText(aP, "p", "",
       "WARNING: the 'heap-allocated' memory reporter and the " +
       "moz_malloc_usable_size() function do not work for this platform " +
       "and/or configuration.  This means that 'heap-unclassified' is not " +
       "shown and the 'explicit' tree shows much less memory than it should.\n\n");
   } else if (!aHasKnownHeapAllocated) {
     appendElementWithText(aP, "p", "",
       "WARNING: the 'heap-allocated' memory reporter does not work for this " +
       "platform and/or configuration. This means that 'heap-unclassified' " +
       "is not shown and the 'explicit' tree shows less memory than it should.\n\n");
   } else if (!aHasMozMallocUsableSize) {
     appendElementWithText(aP, "p", "",
       "WARNING: the moz_malloc_usable_size() function does not work for " +
       "this platform and/or configuration.  This means that much of the " +
       "heap-allocated memory is not measured by individual memory reporters " +
       "and so will fall under 'heap-unclassified'.\n\n");
   }
   if (gUnsafePathsWithInvalidValuesForThisProcess.length > 0) {
     let div = appendElement(aP, "div");
     appendElementWithText(div, "p", "",
       "WARNING: the following values are negative or unreasonably large.\n");
     let ul = appendElement(div, "ul");
     for (let i = 0;
          i < gUnsafePathsWithInvalidValuesForThisProcess.length;
          i++)
     {
       appendTextNode(ul, " ");
       appendElementWithText(ul, "li", "",
         flipBackslashes(gUnsafePathsWithInvalidValuesForThisProcess[i]) + "\n");
     }
     appendElementWithText(div, "p", "",
       "This indicates a defect in one or more memory reporters.  The " +
       "invalid values are highlighted.\n\n");
     gUnsafePathsWithInvalidValuesForThisProcess = [];  // reset for the next process
   }
 }
 /**
  * Appends the about:memory elements for a single process.
  *
  * @param aP
  *        The parent DOM node.
  * @param aN
  *        The number of the process, starting at 0.
  * @param aProcess
  *        The name of the process.
  * @param aTrees
  *        The table of non-degenerate trees for this process.
  * @param aDegenerates
  *        The table of degenerate trees for this process.
  * @param aHasMozMallocUsableSize
  *        Boolean indicating if moz_malloc_usable_size works.
  * @return The generated text.
  */
 function appendProcessAboutMemoryElements(aP, aN, aProcess, aTrees,
                                           aDegenerates, aHeapTotal,
                                           aHasMozMallocUsableSize)
 {
   const kUpwardsArrow   = "\u2191",
         kDownwardsArrow = "\u2193";
   let appendLink = function(aHere, aThere, aArrow) {
     let link = appendElementWithText(aP, "a", "upDownArrow", aArrow);
     link.href = "#" + aThere + aN;
     link.id = aHere + aN;
     link.title = "Go to the " + aThere + " of " + aProcess;
     link.style = "text-decoration: none";
     // This jumps to the anchor without the page location getting the anchor
     // name tacked onto its end, which is what happens with a vanilla link.
     link.addEventListener("click", function(event) {
       document.documentElement.scrollTop =
         document.querySelector(event.target.href).offsetTop;
       event.preventDefault();
     }, false);
     // This gives nice spacing when we copy and paste.
     appendElementWithText(aP, "span", "", "\n");
   }
   appendElementWithText(aP, "h1", "", aProcess);
   appendLink("start", "end", kDownwardsArrow);
   // We'll fill this in later.
   let warningsDiv = appendElement(aP, "div", "accuracyWarning");
   // The explicit tree.
   let hasExplicitTree;
   let hasKnownHeapAllocated;
   {
     let treeName = "explicit";
     let t = aTrees[treeName];
     if (t) {
       let pre = appendSectionHeader(aP, "Explicit Allocations");
       hasExplicitTree = true;
       fillInTree(t);
       // Using the "heap-allocated" reporter here instead of
       // nsMemoryReporterManager.heapAllocated goes against the usual pattern.
       // But the "heap-allocated" node will go in the tree like the others, so
       // we have to deal with it, and once we're dealing with it, it's easier
       // to keep doing so rather than switching to the distinguished amount.
       hasKnownHeapAllocated =
         aDegenerates &&
         addHeapUnclassifiedNode(t, aDegenerates["heap-allocated"], aHeapTotal);
       sortTreeAndInsertAggregateNodes(t._amount, t);
       t._description = explicitTreeDescription;
       appendTreeElements(pre, t, aProcess, "");
       delete aTrees[treeName];
     }
     appendTextNode(aP, "\n");  // gives nice spacing when we copy and paste
   }
   // Fill in and sort all the non-degenerate other trees.
   let otherTrees = [];
   for (let unsafeName in aTrees) {
     let t = aTrees[unsafeName];
     assert(!t._isDegenerate, "tree is degenerate");
     fillInTree(t);
     sortTreeAndInsertAggregateNodes(t._amount, t);
     otherTrees.push(t);
   }
   otherTrees.sort(TreeNode.compareUnsafeNames);
   // Get the length of the longest root value among the degenerate other trees,
   // and sort them as well.
   let otherDegenerates = [];
   let maxStringLength = 0;
   for (let unsafeName in aDegenerates) {
     let t = aDegenerates[unsafeName];
     assert(t._isDegenerate, "tree is not degenerate");
     let length = t.toString().length;
     if (length > maxStringLength) {
       maxStringLength = length;
     }
     otherDegenerates.push(t);
   }
   otherDegenerates.sort(TreeNode.compareUnsafeNames);
   // Now generate the elements, putting non-degenerate trees first.
   let pre = appendSectionHeader(aP, "Other Measurements");
   for (let i = 0; i < otherTrees.length; i++) {
     let t = otherTrees[i];
     appendTreeElements(pre, t, aProcess, "");
     appendTextNode(pre, "\n");  // blank lines after non-degenerate trees
   }
   for (let i = 0; i < otherDegenerates.length; i++) {
     let t = otherDegenerates[i];
     let padText = pad("", maxStringLength - t.toString().length, ' ');
     appendTreeElements(pre, t, aProcess, padText);
   }
   appendTextNode(aP, "\n");  // gives nice spacing when we copy and paste
   // Add any warnings about inaccuracies in the "explicit" tree due to platform
   // limitations.  These must be computed after generating all the text.  The
   // newlines give nice spacing if we copy+paste into a text buffer.
   if (hasExplicitTree) {
     appendWarningElements(warningsDiv, hasKnownHeapAllocated,
                           aHasMozMallocUsableSize);
   }
   appendElementWithText(aP, "h3", "", "End of " + aProcess);
   appendLink("end", "start", kUpwardsArrow);
 }
 /**
  * Determines if a number has a negative sign when converted to a string.
  * Works even for -0.
  *
  * @param aN
  *        The number.
  * @return A boolean.
  */
 function hasNegativeSign(aN)
 {
   if (aN === 0) {                   // this succeeds for 0 and -0
     return 1 / aN === -Infinity;    // this succeeds for -0
   }
   return aN < 0;
 }
 /**
  * Formats an int as a human-readable string.
  *
  * @param aN
  *        The integer to format.
  * @param aExtra
  *        An extra string to tack onto the end.
  * @return A human-readable string representing the int.
  *
  * Note: building an array of chars and converting that to a string with
  * Array.join at the end is more memory efficient than using string
  * concatenation.  See bug 722972 for details.
  */
 function formatInt(aN, aExtra)
 {
   let neg = false;
   if (hasNegativeSign(aN)) {
     neg = true;
     aN = -aN;
   }
   let s = [];
   while (true) {
     let k = aN % 1000;
     aN = Math.floor(aN / 1000);
     if (aN > 0) {
       if (k < 10) {
         s.unshift(",00", k);
       } else if (k < 100) {
         s.unshift(",0", k);
       } else {
         s.unshift(",", k);
       }
     } else {
       s.unshift(k);
       break;
     }
   }
   if (neg) {
     s.unshift("-");
   }
   if (aExtra) {
     s.push(aExtra);
   }
   return s.join("");
 }
 /**
  * Converts a byte count to an appropriate string representation.
  *
  * @param aBytes
  *        The byte count.
  * @return The string representation.
  */
 function formatBytes(aBytes)
 {
   let unit = gVerbose.checked ? " B" : " MB";
   let s;
   if (gVerbose.checked) {
     s = formatInt(aBytes, unit);
   } else {
     let mbytes = (aBytes / (1024 * 1024)).toFixed(2);
     let a = String(mbytes).split(".");
     // If the argument to formatInt() is -0, it will print the negative sign.
     s = formatInt(Number(a[0])) + "." + a[1] + unit;
   }
   return s;
 }
 /**
  * Converts a percentage to an appropriate string representation.
  *
  * @param aPerc100x
  *        The percentage, multiplied by 100 (see nsIMemoryReporter).
  * @return The string representation
  */
 function formatPercentage(aPerc100x)
 {
   return (aPerc100x / 100).toFixed(2) + "%";
 }
 /**
  * Right-justifies a string in a field of a given width, padding as necessary.
  *
  * @param aS
  *        The string.
  * @param aN
  *        The field width.
  * @param aC
  *        The char used to pad.
  * @return The string representation.
  */
 function pad(aS, aN, aC)
 {
   let padding = "";
   let n2 = aN - aS.length;
   for (let i = 0; i < n2; i++) {
     padding += aC;
   }
   return padding + aS;
 }
 // There's a subset of the Unicode "light" box-drawing chars that is widely
 // implemented in terminals, and this code sticks to that subset to maximize
 // the chance that copying and pasting about:memory output to a terminal will
 // work correctly.
 const kHorizontal                   = "\u2500",
       kVertical                     = "\u2502",
       kUpAndRight                   = "\u2514",
       kUpAndRight_Right_Right       = "\u2514\u2500\u2500",
       kVerticalAndRight             = "\u251c",
       kVerticalAndRight_Right_Right = "\u251c\u2500\u2500",
       kVertical_Space_Space         = "\u2502  ";
 const kNoKidsSep                    = " \u2500\u2500 ",
       kHideKidsSep                  = " ++ ",
       kShowKidsSep                  = " -- ";
 function appendMrNameSpan(aP, aDescription, aUnsafeName, aIsInvalid, aNMerged,
                           aPresence)
 {
   let safeName = flipBackslashes(aUnsafeName);
   if (!aIsInvalid && !aNMerged && !aPresence) {
     safeName += "\n";
   }
   let nameSpan = appendElementWithText(aP, "span", "mrName", safeName);
   nameSpan.title = aDescription;
   if (aIsInvalid) {
     let noteText = " [?!]";
     if (!aNMerged) {
       noteText += "\n";
     }
     let noteSpan = appendElementWithText(aP, "span", "mrNote", noteText);
     noteSpan.title =
       "Warning: this value is invalid and indicates a bug in one or more " +
       "memory reporters. ";
   }
   if (aNMerged) {
     let noteText = " [" + aNMerged + "]";
     if (!aPresence) {
       noteText += "\n";
     }
     let noteSpan = appendElementWithText(aP, "span", "mrNote", noteText);
     noteSpan.title =
       "This value is the sum of " + aNMerged +
       " memory reports that all have the same path.";
   }
   if (aPresence) {
     let c, title;
     switch (aPresence) {
      case DReport.PRESENT_IN_FIRST_ONLY:
       c = '-';
       title = "This value was only present in the first set of memory reports.";
       break;
      case DReport.PRESENT_IN_SECOND_ONLY:
       c = '+';
       title = "This value was only present in the second set of memory reports.";
       break;
      case DReport.ADDED_FOR_BALANCE:
       c = '!';
       title = "One of the sets of memory reports lacked children for this " +
               "node's parent. This is a fake child node added to make the " +
               "two memory sets comparable.";
       break;
      default: assert(false, "bad presence");
       break;
     }
     let noteSpan = appendElementWithText(aP, "span", "mrNote",
                                          " [" + c + "]\n");
     noteSpan.title = title;
   }
 }
 // This is used to record the (safe) IDs of which sub-trees have been manually
 // expanded (marked as true) and collapsed (marked as false).  It's used to
 // replicate the collapsed/expanded state when the page is updated.  It can end
 // up holding IDs of nodes that no longer exist, e.g. for compartments that
 // have been closed.  This doesn't seem like a big deal, because the number is
 // limited by the number of entries the user has changed from their original
 // state.
 let gShowSubtreesBySafeTreeId = {};
 function assertClassListContains(e, className) {
   assert(e, "undefined " + className);
   assert(e.classList.contains(className), "classname isn't " + className);
 }
 function toggle(aEvent)
 {
   // This relies on each line being a span that contains at least four spans:
   // mrValue, mrPerc, mrSep, mrName, and then zero or more mrNotes.  All
   // whitespace must be within one of these spans for this function to find the
   // right nodes.  And the span containing the children of this line must
   // immediately follow.  Assertions check this.
   // |aEvent.target| will be one of the spans.  Get the outer span.
   let outerSpan = aEvent.target.parentNode;
   assertClassListContains(outerSpan, "hasKids");
   // Toggle the '++'/'--' separator.
   let isExpansion;
   let sepSpan = outerSpan.childNodes[2];
   assertClassListContains(sepSpan, "mrSep");
   if (sepSpan.textContent === kHideKidsSep) {
     isExpansion = true;
     sepSpan.textContent = kShowKidsSep;
   } else if (sepSpan.textContent === kShowKidsSep) {
     isExpansion = false;
     sepSpan.textContent = kHideKidsSep;
   } else {
     assert(false, "bad sepSpan textContent");
   }
   // Toggle visibility of the span containing this node's children.
   let subTreeSpan = outerSpan.nextSibling;
   assertClassListContains(subTreeSpan, "kids");
   subTreeSpan.classList.toggle("hidden");
   // Record/unrecord that this sub-tree was toggled.
   let safeTreeId = outerSpan.id;
   if (gShowSubtreesBySafeTreeId[safeTreeId] !== undefined) {
     delete gShowSubtreesBySafeTreeId[safeTreeId];
   } else {
     gShowSubtreesBySafeTreeId[safeTreeId] = isExpansion;
   }
 }
 function expandPathToThisElement(aElement)
 {
   if (aElement.classList.contains("kids")) {
     // Unhide the kids.
     aElement.classList.remove("hidden");
     expandPathToThisElement(aElement.previousSibling);  // hasKids
   } else if (aElement.classList.contains("hasKids")) {
     // Change the separator to '--'.
     let sepSpan = aElement.childNodes[2];
     assertClassListContains(sepSpan, "mrSep");
     sepSpan.textContent = kShowKidsSep;
     expandPathToThisElement(aElement.parentNode);       // kids or pre.entries
   } else {
     assertClassListContains(aElement, "entries");
   }
 }
 /**
  * Appends the elements for the tree, including its heading.
  *
  * @param aP
  *        The parent DOM node.
  * @param aRoot
  *        The tree root.
  * @param aProcess
  *        The process the tree corresponds to.
  * @param aPadText
  *        A string to pad the start of each entry.
  */
 function appendTreeElements(aP, aRoot, aProcess, aPadText)
 {
   /**
    * Appends the elements for a particular tree, without a heading.
    *
    * @param aP
    *        The parent DOM node.
    * @param aProcess
    *        The process the tree corresponds to.
    * @param aUnsafeNames
    *        An array of the names forming the path to aT.
    * @param aRoot
    *        The root of the tree this sub-tree belongs to.
    * @param aT
    *        The tree.
    * @param aTreelineText1
    *        The first part of the treeline for this entry and this entry's
    *        children.
    * @param aTreelineText2a
    *        The second part of the treeline for this entry.
    * @param aTreelineText2b
    *        The second part of the treeline for this entry's children.
    * @param aParentStringLength
    *        The length of the formatted byte count of the top node in the tree.
    */
   function appendTreeElements2(aP, aProcess, aUnsafeNames, aRoot, aT,
                                aTreelineText1, aTreelineText2a,
                                aTreelineText2b, aParentStringLength)
   {
     function appendN(aS, aC, aN)
     {
       for (let i = 0; i < aN; i++) {
         aS += aC;
       }
       return aS;
     }
     // The tree line.  Indent more if this entry is narrower than its parent.
     let valueText = aT.toString();
     let extraTreelineLength =
       Math.max(aParentStringLength - valueText.length, 0);
     if (extraTreelineLength > 0) {
       aTreelineText2a =
         appendN(aTreelineText2a, kHorizontal, extraTreelineLength);
       aTreelineText2b =
         appendN(aTreelineText2b, " ",         extraTreelineLength);
     }
     let treelineText = aTreelineText1 + aTreelineText2a;
     appendElementWithText(aP, "span", "treeline", treelineText);
     // Detect and record invalid values.  But not if gIsDiff is true, because
     // we expect negative values in that case.
     assertInput(aRoot._units === aT._units,
                 "units within a tree are inconsistent");
     let tIsInvalid = false;
     if (!gIsDiff && !(0 <= aT._amount && aT._amount <= aRoot._amount)) {
       tIsInvalid = true;
       let unsafePath = aUnsafeNames.join("/");
       gUnsafePathsWithInvalidValuesForThisProcess.push(unsafePath);
       reportAssertionFailure("Invalid value (" + aT._amount + " / " +
                              aRoot._amount + ") for " +
                              flipBackslashes(unsafePath));
     }
     // For non-leaf nodes, the entire sub-tree is put within a span so it can
     // be collapsed if the node is clicked on.
     let d;
     let sep;
     let showSubtrees;
     if (aT._kids) {
       // Determine if we should show the sub-tree below this entry;  this
       // involves reinstating any previous toggling of the sub-tree.
       let unsafePath = aUnsafeNames.join("/");
       let safeTreeId = aProcess + ":" + flipBackslashes(unsafePath);
       showSubtrees = !aT._hideKids;
       if (gShowSubtreesBySafeTreeId[safeTreeId] !== undefined) {
         showSubtrees = gShowSubtreesBySafeTreeId[safeTreeId];
       }
       d = appendElement(aP, "span", "hasKids");
       d.id = safeTreeId;
       d.onclick = toggle;
       sep = showSubtrees ? kShowKidsSep : kHideKidsSep;
     } else {
       assert(!aT._hideKids, "leaf node with _hideKids set")
       sep = kNoKidsSep;
       d = aP;
     }
     // The value.
     appendElementWithText(d, "span", "mrValue" + (tIsInvalid ? " invalid" : ""),
                           valueText);
     // The percentage (omitted for single entries).
     let percText;
     if (!aT._isDegenerate) {
       // Treat 0 / 0 as 100%.
       let num = aRoot._amount === 0 ? 100 : (100 * aT._amount / aRoot._amount);
       let numText = num.toFixed(2);
       percText = numText === "100.00"
                ? " (100.0%)"
                : (0 <= num && num < 10 ? " (0" : " (") + numText + "%)";
       appendElementWithText(d, "span", "mrPerc", percText);
     }
     // The separator.
     appendElementWithText(d, "span", "mrSep", sep);
     // The entry's name.
     appendMrNameSpan(d, aT._description, aT._unsafeName,
                      tIsInvalid, aT._nMerged, aT._presence);
     // In non-verbose mode, invalid nodes can be hidden in collapsed sub-trees.
     // But it's good to always see them, so force this.
     if (!gVerbose.checked && tIsInvalid) {
       expandPathToThisElement(d);
     }
     // Recurse over children.
     if (aT._kids) {
       // The 'kids' class is just used for sanity checking in toggle().
       d = appendElement(aP, "span", showSubtrees ? "kids" : "kids hidden");
       let kidTreelineText1 = aTreelineText1 + aTreelineText2b;
       for (let i = 0; i < aT._kids.length; i++) {
         let kidTreelineText2a, kidTreelineText2b;
         if (i < aT._kids.length - 1) {
           kidTreelineText2a = kVerticalAndRight_Right_Right;
           kidTreelineText2b = kVertical_Space_Space;
         } else {
           kidTreelineText2a = kUpAndRight_Right_Right;
           kidTreelineText2b = "   ";
         }
         aUnsafeNames.push(aT._kids[i]._unsafeName);
         appendTreeElements2(d, aProcess, aUnsafeNames, aRoot, aT._kids[i],
                             kidTreelineText1, kidTreelineText2a,
                             kidTreelineText2b, valueText.length);
         aUnsafeNames.pop();
       }
     }
   }
   let rootStringLength = aRoot.toString().length;
   appendTreeElements2(aP, aProcess, [aRoot._unsafeName], aRoot, aRoot,
                       aPadText, "", "", rootStringLength);
 }
 //---------------------------------------------------------------------------
 function appendSectionHeader(aP, aText)
 {
   appendElementWithText(aP, "h2", "", aText + "\n");
   return appendElement(aP, "pre", "entries");
 }
 //---------------------------------------------------------------------------
 function saveReportsToFile()
 {
   let fp = Cc["@mozilla.org/filepicker;1"].createInstance(Ci.nsIFilePicker);
   fp.appendFilter("Zipped JSON files", "*.json.gz");
   fp.appendFilters(Ci.nsIFilePicker.filterAll);
   fp.filterIndex = 0;
   fp.addToRecentDocs = true;
   fp.defaultString = "memory-report.json.gz";
   let fpFinish = function(file) {
     let dumper = Cc["@mozilla.org/memory-info-dumper;1"]
                    .getService(Ci.nsIMemoryInfoDumper);
     let finishDumping = () => {
       updateMainAndFooter("Saved reports to " + file.path, HIDE_FOOTER);
     }
     dumper.dumpMemoryReportsToNamedFile(file.path, finishDumping, null);
   }
   let fpCallback = function(aResult) {
     if (aResult == Ci.nsIFilePicker.returnOK ||
         aResult == Ci.nsIFilePicker.returnReplace) {
       fpFinish(fp.file);
     }
   };
   try {
     fp.init(window, "Save Memory Reports", Ci.nsIFilePicker.modeSave);
   } catch(ex) {
     // This will fail on Android, since there is no Save as file picker there.
     // Just save to the default downloads dir if it does.
     let file = Services.dirsvc.get("DfltDwnld", Ci.nsIFile);
     file.append(fp.defaultString);
     fpFinish(file);
     return;
   }
   fp.open(fpCallback);
 }