The Tor Browser: b2g/chrome/content/settings.js@6474c204b198 (annotated)

b2g/chrome/content/settings.js@6474c204b198 (annotated)

b2g/chrome/content/settings.js

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /* -*- Mode: Java; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- /
 /* vim: set shiftwidth=2 tabstop=2 autoindent cindent expandtab: */
 /* 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/. */
 "use strict;"
 const Cc = Components.classes;
 const Ci = Components.interfaces;
 const Cu = Components.utils;
 const Cr = Components.results;
 Cu.import('resource://gre/modules/XPCOMUtils.jsm');
 Cu.import('resource://gre/modules/Services.jsm');
 #ifdef MOZ_WIDGET_GONK
 XPCOMUtils.defineLazyGetter(this, "libcutils", function () {
   Cu.import("resource://gre/modules/systemlibs.js");
   return libcutils;
 });
 #endif
 XPCOMUtils.defineLazyServiceGetter(this, "uuidgen",
                                    "@mozilla.org/uuid-generator;1",
                                    "nsIUUIDGenerator");
 // Once Bug 731746 - Allow chrome JS object to implement nsIDOMEventTarget
 // is resolved this helper could be removed.
 var SettingsListener = {
   _callbacks: {},
   init: function sl_init() {
     if ('mozSettings' in navigator && navigator.mozSettings) {
       navigator.mozSettings.onsettingchange = this.onchange.bind(this);
     }
   },
   onchange: function sl_onchange(evt) {
     var callback = this._callbacks[evt.settingName];
     if (callback) {
       callback(evt.settingValue);
     }
   },
   observe: function sl_observe(name, defaultValue, callback) {
     var settings = window.navigator.mozSettings;
     if (!settings) {
       window.setTimeout(function() { callback(defaultValue); });
       return;
     }
     if (!callback || typeof callback !== 'function') {
       throw new Error('Callback is not a function');
     }
     var req = settings.createLock().get(name);
     req.addEventListener('success', (function onsuccess() {
       callback(typeof(req.result[name]) != 'undefined' ?
         req.result[name] : defaultValue);
     }));
     this._callbacks[name] = callback;
   }
 };
 SettingsListener.init();
 // =================== Console ======================
 SettingsListener.observe('debug.console.enabled', true, function(value) {
   Services.prefs.setBoolPref('consoleservice.enabled', value);
   Services.prefs.setBoolPref('layout.css.report_errors', value);
 });
 // =================== Languages ====================
 SettingsListener.observe('language.current', 'en-US', function(value) {
   Services.prefs.setCharPref('general.useragent.locale', value);
   let prefName = 'intl.accept_languages';
   if (Services.prefs.prefHasUserValue(prefName)) {
     Services.prefs.clearUserPref(prefName);
   }
   let intl = '';
   try {
     intl = Services.prefs.getComplexValue(prefName,
                                           Ci.nsIPrefLocalizedString).data;
   } catch(e) {}
   // Bug 830782 - Homescreen is in English instead of selected locale after
   // the first run experience.
   // In order to ensure the current intl value is reflected on the child
   // process let's always write a user value, even if this one match the
   // current localized pref value.
   if (!((new RegExp('^' + value + '[^a-z-_] *[,;]?', 'i')).test(intl))) {
     value = value + ', ' + intl;
   } else {
     value = intl;
   }
   Services.prefs.setCharPref(prefName, value);
   if (shell.hasStarted() == false) {
     shell.start();
   }
 });
 // =================== RIL ====================
 (function RILSettingsToPrefs() {
   let strPrefs = ['ril.mms.mmsc', 'ril.mms.mmsproxy'];
   strPrefs.forEach(function(key) {
     SettingsListener.observe(key, "", function(value) {
       Services.prefs.setCharPref(key, value);
     });
   });
   ['ril.mms.mmsport'].forEach(function(key) {
     SettingsListener.observe(key, null, function(value) {
       if (value != null) {
         Services.prefs.setIntPref(key, value);
       }
     });
   });
   // DSDS default service IDs
   ['mms', 'sms', 'telephony', 'voicemail'].forEach(function(key) {
     SettingsListener.observe('ril.' + key + '.defaultServiceId', 0,
                              function(value) {
       if (value != null) {
         Services.prefs.setIntPref('dom.' + key + '.defaultServiceId', value);
       }
     });
   });
 })();
 //=================== DeviceInfo ====================
 Components.utils.import('resource://gre/modules/XPCOMUtils.jsm');
 Components.utils.import('resource://gre/modules/ctypes.jsm');
 (function DeviceInfoToSettings() {
   // MOZ_B2G_VERSION is set in b2g/confvars.sh, and is output as a #define value
   // from configure.in, defaults to 1.0.0 if this value is not exist.
 #filter attemptSubstitution
   let os_version = '@MOZ_B2G_VERSION@';
   let os_name = '@MOZ_B2G_OS_NAME@';
 #unfilter attemptSubstitution
   let appInfo = Cc["@mozilla.org/xre/app-info;1"]
                   .getService(Ci.nsIXULAppInfo);
   // Get the hardware info and firmware revision from device properties.
   let hardware_info = null;
   let firmware_revision = null;
   let product_model = null;
 #ifdef MOZ_WIDGET_GONK
     hardware_info = libcutils.property_get('ro.hardware');
     firmware_revision = libcutils.property_get('ro.firmware_revision');
     product_model = libcutils.property_get('ro.product.model');
 #endif
   let software = os_name + ' ' + os_version;
   let setting = {
     'deviceinfo.os': os_version,
     'deviceinfo.software': software,
     'deviceinfo.platform_version': appInfo.platformVersion,
     'deviceinfo.platform_build_id': appInfo.platformBuildID,
     'deviceinfo.hardware': hardware_info,
     'deviceinfo.firmware_revision': firmware_revision,
     'deviceinfo.product_model': product_model
   }
   window.navigator.mozSettings.createLock().set(setting);
 })();
 // =================== DevTools ====================
 let developerHUD;
 SettingsListener.observe('devtools.overlay', false, (value) => {
   if (value) {
     if (!developerHUD) {
       let scope = {};
       Services.scriptloader.loadSubScript('chrome://b2g/content/devtools.js', scope);
       developerHUD = scope.developerHUD;
     }
     developerHUD.init();
   } else {
     if (developerHUD) {
       developerHUD.uninit();
     }
   }
 });
 // =================== Debugger / ADB ====================
 #ifdef MOZ_WIDGET_GONK
 let AdbController = {
   DEBUG: false,
   locked: undefined,
   remoteDebuggerEnabled: undefined,
   lockEnabled: undefined,
   disableAdbTimer: null,
   disableAdbTimeoutHours: 12,
   umsActive: false,
   debug: function(str) {
     dump("AdbController: " + str + "\n");
   },
   setLockscreenEnabled: function(value) {
     this.lockEnabled = value;
     if (this.DEBUG) {
       this.debug("setLockscreenEnabled = " + this.lockEnabled);
     }
     this.updateState();
   },
   setLockscreenState: function(value) {
     this.locked = value;
     if (this.DEBUG) {
       this.debug("setLockscreenState = " + this.locked);
     }
     this.updateState();
   },
   setRemoteDebuggerState: function(value) {
     this.remoteDebuggerEnabled = value;
     if (this.DEBUG) {
       this.debug("setRemoteDebuggerState = " + this.remoteDebuggerEnabled);
     }
     this.updateState();
   },
   startDisableAdbTimer: function() {
     if (this.disableAdbTimer) {
       this.disableAdbTimer.cancel();
     } else {
       this.disableAdbTimer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
       try {
         this.disableAdbTimeoutHours =
           Services.prefs.getIntPref("b2g.adb.timeout-hours");
       } catch (e) {
         // This happens if the pref doesn't exist, in which case
         // disableAdbTimeoutHours will still be set to the default.
       }
     }
     if (this.disableAdbTimeoutHours <= 0) {
       if (this.DEBUG) {
         this.debug("Timer to disable ADB not started due to zero timeout");
       }
       return;
     }
     if (this.DEBUG) {
       this.debug("Starting timer to disable ADB in " +
                  this.disableAdbTimeoutHours + " hours");
     }
     let timeoutMilliseconds = this.disableAdbTimeoutHours * 60 * 60 * 1000;
     this.disableAdbTimer.initWithCallback(this, timeoutMilliseconds,
                                           Ci.nsITimer.TYPE_ONE_SHOT);
   },
   stopDisableAdbTimer: function() {
     if (this.DEBUG) {
       this.debug("Stopping timer to disable ADB");
     }
     if (this.disableAdbTimer) {
       this.disableAdbTimer.cancel();
       this.disableAdbTimer = null;
     }
   },
   notify: function(aTimer) {
     if (aTimer == this.disableAdbTimer) {
       this.disableAdbTimer = null;
       // The following dump will be the last thing that shows up in logcat,
       // and will at least give the user a clue about why logcat was
       // disconnected, if the user happens to be using logcat.
       dump("AdbController: ADB timer expired - disabling ADB\n");
       navigator.mozSettings.createLock().set(
         {'devtools.debugger.remote-enabled': false});
     }
   },
   updateState: function() {
     this.umsActive = false;
     this.storages = navigator.getDeviceStorages('sdcard');
     this.updateStorageState(0);
   },
   updateStorageState: function(storageIndex) {
     if (storageIndex >= this.storages.length) {
       // We've iterated through all of the storage objects, now we can
       // really do updateStateInternal.
       this.updateStateInternal();
       return;
     }
     let storage = this.storages[storageIndex];
     if (this.DEBUG) {
       this.debug("Checking availability of storage: '" +
                  storage.storageName);
     }
     let req = storage.available();
     req.onsuccess = function(e) {
       if (this.DEBUG) {
         this.debug("Storage: '" + storage.storageName + "' is '" +
                    e.target.result);
       }
       if (e.target.result == 'shared') {
         // We've found a storage area that's being shared with the PC.
         // We can stop looking now.
         this.umsActive = true;
         this.updateStateInternal();
         return;
       }
       this.updateStorageState(storageIndex + 1);
     }.bind(this);
     req.onerror = function(e) {
       dump("AdbController: error querying storage availability for '" +
            this.storages[storageIndex].storageName + "' (ignoring)\n");
       this.updateStorageState(storageIndex + 1);
     }.bind(this);
   },
   updateStateInternal: function() {
     if (this.DEBUG) {
       this.debug("updateStateInternal: called");
     }
     if (this.remoteDebuggerEnabled === undefined ||
         this.lockEnabled === undefined ||
         this.locked === undefined) {
       // Part of initializing the settings database will cause the observers
       // to trigger. We want to wait until both have been initialized before
       // we start changing ther adb state. Without this then we can wind up
       // toggling adb off and back on again (or on and back off again).
       //
       // For completeness, one scenario which toggles adb is using the unagi.
       // The unagi has adb enabled by default (prior to b2g starting). If you
       // have the phone lock disabled and remote debugging enabled, then we'll
       // receive an unlock event and an rde event. However at the time we
       // receive the unlock event we haven't yet received the rde event, so
       // we turn adb off momentarily, which disconnects a logcat that might
       // be running. Changing the defaults (in AdbController) just moves the
       // problem to a different phone, which has adb disabled by default and
       // we wind up turning on adb for a short period when we shouldn't.
       //
       // By waiting until both values are properly initialized, we avoid
       // turning adb on or off accidentally.
       if (this.DEBUG) {
         this.debug("updateState: Waiting for all vars to be initialized");
       }
       return;
     }
     // Check if we have a remote debugging session going on. If so, we won't
     // disable adb even if the screen is locked.
     let isDebugging = RemoteDebugger.isDebugging;
     if (this.DEBUG) {
       this.debug("isDebugging=" + isDebugging);
     }
     // If USB Mass Storage, USB tethering, or a debug session is active,
     // then we don't want to disable adb in an automatic fashion (i.e.
     // when the screen locks or due to timeout).
     let sysUsbConfig = libcutils.property_get("sys.usb.config");
     let rndisActive = (sysUsbConfig.split(",").indexOf("rndis") >= 0);
     let usbFuncActive = rndisActive || this.umsActive || isDebugging;
     let enableAdb = this.remoteDebuggerEnabled &&
       (!(this.lockEnabled && this.locked) || usbFuncActive);
     let useDisableAdbTimer = true;
     try {
       if (Services.prefs.getBoolPref("marionette.defaultPrefs.enabled")) {
         // Marionette is enabled. Marionette requires that adb be on (and also
         // requires that remote debugging be off). The fact that marionette
         // is enabled also implies that we're doing a non-production build, so
         // we want adb enabled all of the time.
         enableAdb = true;
         useDisableAdbTimer = false;
       }
     } catch (e) {
       // This means that the pref doesn't exist. Which is fine. We just leave
       // enableAdb alone.
     }
     if (this.DEBUG) {
       this.debug("updateState: enableAdb = " + enableAdb +
                  " remoteDebuggerEnabled = " + this.remoteDebuggerEnabled +
                  " lockEnabled = " + this.lockEnabled +
                  " locked = " + this.locked +
                  " usbFuncActive = " + usbFuncActive);
     }
     // Configure adb.
     let currentConfig = libcutils.property_get("persist.sys.usb.config");
     let configFuncs = currentConfig.split(",");
     let adbIndex = configFuncs.indexOf("adb");
     if (enableAdb) {
       // Add adb to the list of functions, if not already present
       if (adbIndex < 0) {
         configFuncs.push("adb");
       }
     } else {
       // Remove adb from the list of functions, if present
       if (adbIndex >= 0) {
         configFuncs.splice(adbIndex, 1);
       }
     }
     let newConfig = configFuncs.join(",");
     if (newConfig != currentConfig) {
       if (this.DEBUG) {
         this.debug("updateState: currentConfig = " + currentConfig);
         this.debug("updateState:     newConfig = " + newConfig);
       }
       try {
         libcutils.property_set("persist.sys.usb.config", newConfig);
       } catch(e) {
         dump("Error configuring adb: " + e);
       }
     }
     if (useDisableAdbTimer) {
       if (enableAdb && !usbFuncActive) {
         this.startDisableAdbTimer();
       } else {
         this.stopDisableAdbTimer();
       }
     }
   }
 };
 SettingsListener.observe("lockscreen.locked", false,
                          AdbController.setLockscreenState.bind(AdbController));
 SettingsListener.observe("lockscreen.enabled", false,
                          AdbController.setLockscreenEnabled.bind(AdbController));
 #endif
 // Keep the old setting to not break people that won't have updated
 // gaia and gecko.
 SettingsListener.observe('devtools.debugger.remote-enabled', false, function(value) {
   Services.prefs.setBoolPref('devtools.debugger.remote-enabled', value);
   // This preference is consulted during startup
   Services.prefs.savePrefFile(null);
   try {
     value ? RemoteDebugger.start() : RemoteDebugger.stop();
   } catch(e) {
     dump("Error while initializing devtools: " + e + "\n" + e.stack + "\n");
   }
 #ifdef MOZ_WIDGET_GONK
   AdbController.setRemoteDebuggerState(value);
 #endif
 });
 SettingsListener.observe('debugger.remote-mode', false, function(value) {
   if (['disabled', 'adb-only', 'adb-devtools'].indexOf(value) == -1) {
     dump('Illegal value for debugger.remote-mode: ' + value + '\n');
     return;
   }
   Services.prefs.setBoolPref('devtools.debugger.remote-enabled',
                              value == 'adb-devtools');
   // This preference is consulted during startup
   Services.prefs.savePrefFile(null);
   try {
     (value == 'adb-devtools') ? RemoteDebugger.start()
                               : RemoteDebugger.stop();
   } catch(e) {
     dump("Error while initializing devtools: " + e + "\n" + e.stack + "\n");
   }
 #ifdef MOZ_WIDGET_GONK
   AdbController.setRemoteDebuggerState(value != 'disabled');
 #endif
 });
 // =================== Device Storage ====================
 SettingsListener.observe('device.storage.writable.name', 'sdcard', function(value) {
   if (Services.prefs.getPrefType('device.storage.writable.name') != Ci.nsIPrefBranch.PREF_STRING) {
     // We clear the pref because it used to be erroneously written as a bool
     // and we need to clear it before we can change it to have the correct type.
     Services.prefs.clearUserPref('device.storage.writable.name');
   }
   Services.prefs.setCharPref('device.storage.writable.name', value);
 });
 // =================== Privacy ====================
 SettingsListener.observe('privacy.donottrackheader.value', 1, function(value) {
   Services.prefs.setIntPref('privacy.donottrackheader.value', value);
   // If the user specifically disallows tracking, we set the value of
   // app.update.custom (update tracking ID) to an empty string.
   if (value == 1) {
     Services.prefs.setCharPref('app.update.custom', '');
     return;
   }
   // Otherwise, we assure that the update tracking ID exists.
   setUpdateTrackingId();
 });
 // =================== Crash Reporting ====================
 SettingsListener.observe('app.reportCrashes', 'ask', function(value) {
   if (value == 'always') {
     Services.prefs.setBoolPref('app.reportCrashes', true);
   } else if (value == 'never') {
     Services.prefs.setBoolPref('app.reportCrashes', false);
   } else {
     Services.prefs.clearUserPref('app.reportCrashes');
   }
   // This preference is consulted during startup.
   Services.prefs.savePrefFile(null);
 });
 // ================ Updates ================
 /**
  * For tracking purposes some partners require us to add an UUID to the
  * update URL. The update tracking ID will be an empty string if the
  * do-not-track feature specifically disallows tracking and it is reseted
  * to a different ID if the do-not-track value changes from disallow to allow.
  */
 function setUpdateTrackingId() {
   try {
     let dntEnabled = Services.prefs.getBoolPref('privacy.donottrackheader.enabled');
     let dntValue =  Services.prefs.getIntPref('privacy.donottrackheader.value');
     // If the user specifically decides to disallow tracking (1), we just bail out.
     if (dntEnabled && (dntValue == 1)) {
       return;
     }
     let trackingId =
       Services.prefs.getPrefType('app.update.custom') ==
       Ci.nsIPrefBranch.PREF_STRING &&
       Services.prefs.getCharPref('app.update.custom');
     // If there is no previous registered tracking ID, we generate a new one.
     // This should only happen on first usage or after changing the
     // do-not-track value from disallow to allow.
     if (!trackingId) {
       trackingId = uuidgen.generateUUID().toString().replace(/[{}]/g, "");
       Services.prefs.setCharPref('app.update.custom', trackingId);
     }
   } catch(e) {
     dump('Error getting tracking ID ' + e + '\n');
   }
 }
 setUpdateTrackingId();
 // ================ Debug ================
 (function Composer2DSettingToPref() {
   //layers.composer.enabled can be enabled in three ways
   //In order of precedence they are:
   //
   //1. mozSettings "layers.composer.enabled"
   //2. a gecko pref "layers.composer.enabled"
   //3. presence of ro.display.colorfill at the Gonk level
   var req = navigator.mozSettings.createLock().get('layers.composer2d.enabled');
   req.onsuccess = function() {
     if (typeof(req.result['layers.composer2d.enabled']) === 'undefined') {
       var enabled = false;
       if (Services.prefs.getPrefType('layers.composer2d.enabled') == Ci.nsIPrefBranch.PREF_BOOL) {
         enabled = Services.prefs.getBoolPref('layers.composer2d.enabled');
       } else {
 #ifdef MOZ_WIDGET_GONK
         enabled = (libcutils.property_get('ro.display.colorfill') === '1');
 #endif
       }
       navigator.mozSettings.createLock().set({'layers.composer2d.enabled': enabled });
     }
     SettingsListener.observe("layers.composer2d.enabled", true, function(value) {
       Services.prefs.setBoolPref("layers.composer2d.enabled", value);
     });
   };
   req.onerror = function() {
     dump("Error configuring layers.composer2d.enabled setting");
   };
 })();
 // ================ Accessibility ============
 SettingsListener.observe("accessibility.screenreader", false, function(value) {
   if (value && !("AccessFu" in this)) {
     Cu.import('resource://gre/modules/accessibility/AccessFu.jsm');
     AccessFu.attach(window);
   }
 });
 // ================ Theming ============
 (function themingSettingsListener() {
   let themingPrefs = ['ui.menu', 'ui.menutext', 'ui.infobackground', 'ui.infotext',
                       'ui.window', 'ui.windowtext', 'ui.highlight'];
   themingPrefs.forEach(function(pref) {
     SettingsListener.observe('gaia.' + pref, null, function(value) {
       if (value) {
         Services.prefs.setCharPref(pref, value);
       }
     });
   });
 })();
 // =================== AsyncPanZoom ======================
 SettingsListener.observe('apz.displayport.heuristics', 'default', function(value) {
   // first reset everything to default
   Services.prefs.clearUserPref('apz.velocity_bias');
   Services.prefs.clearUserPref('apz.use_paint_duration');
   Services.prefs.clearUserPref('apz.x_skate_size_multiplier');
   Services.prefs.clearUserPref('apz.y_skate_size_multiplier');
   Services.prefs.clearUserPref('apz.allow-checkerboarding');
   // and then set the things that we want to change
   switch (value) {
   case 'default':
     break;
   case 'center-displayport':
     Services.prefs.setCharPref('apz.velocity_bias', '0.0');
     break;
   case 'perfect-paint-times':
     Services.prefs.setBoolPref('apz.use_paint_duration', false);
     Services.prefs.setCharPref('apz.velocity_bias', '0.32'); // 16/50 (assumes 16ms paint times instead of 50ms)
     break;
   case 'taller-displayport':
     Services.prefs.setCharPref('apz.y_skate_size_multiplier', '3.5');
     break;
   case 'faster-paint':
     Services.prefs.setCharPref('apz.x_skate_size_multiplier', '1.0');
     Services.prefs.setCharPref('apz.y_skate_size_multiplier', '1.5');
     break;
   case 'no-checkerboard':
     Services.prefs.setBoolPref('apz.allow-checkerboarding', false);
     break;
   }
 });
 // =================== Various simple mapping  ======================
 let settingsToObserve = {
   'ril.mms.retrieval_mode': {
     prefName: 'dom.mms.retrieval_mode',
     defaultValue: 'manual'
   },
   'ril.sms.strict7BitEncoding.enabled': {
     prefName: 'dom.sms.strict7BitEncoding',
     defaultValue: false
   },
   'ril.sms.requestStatusReport.enabled': {
     prefName: 'dom.sms.requestStatusReport',
     defaultValue: false
   },
   'ril.mms.requestStatusReport.enabled': {
     prefName: 'dom.mms.requestStatusReport',
     defaultValue: false
   },
   'ril.mms.requestReadReport.enabled': {
     prefName: 'dom.mms.requestReadReport',
     defaultValue: true
   },
   'ril.cellbroadcast.disabled': false,
   'ril.radio.disabled': false,
   'wap.UAProf.url': '',
   'wap.UAProf.tagname': 'x-wap-profile',
   'devtools.eventlooplag.threshold': 100,
   'privacy.donottrackheader.enabled': false,
   'apz.force-enable': {
     prefName: 'dom.browser_frames.useAsyncPanZoom',
     defaultValue: false
   },
   'layers.enable-tiles': true,
   'layers.simple-tiles': false,
   'layers.progressive-paint': false,
   'layers.draw-tile-borders': false,
   'layers.dump': false,
   'debug.fps.enabled': {
     prefName: 'layers.acceleration.draw-fps',
     defaultValue: false
   },
   'debug.paint-flashing.enabled': {
     prefName: 'nglayout.debug.paint_flashing',
     defaultValue: false
   },
   'layers.draw-borders': false,
   'app.update.interval': 86400,
   'app.update.url': {
     resetToPref: true
   },
   'app.update.channel': {
     resetToPref: true
   },
   'debug.log-animations.enabled': {
     prefName: 'layers.offmainthreadcomposition.log-animations',
     defaultValue: false
   }
 };
 for (let key in settingsToObserve) {
   let setting = settingsToObserve[key];
   // Allow setting to contain flags redefining prefName and defaultValue.
   let prefName = setting.prefName || key;
   let defaultValue = setting.defaultValue;
   if (defaultValue === undefined) {
     defaultValue = setting;
   }
   let prefs = Services.prefs;
   // If requested, reset setting value and defaultValue to the pref value.
   if (setting.resetToPref) {
     switch (prefs.getPrefType(prefName)) {
       case Ci.nsIPrefBranch.PREF_BOOL:
         defaultValue = prefs.getBoolPref(prefName);
         break;
       case Ci.nsIPrefBranch.PREF_INT:
         defaultValue = prefs.getIntPref(prefName);
         break;
       case Ci.nsIPrefBranch.PREF_STRING:
         defaultValue = prefs.getCharPref(prefName);
         break;
     }
     let setting = {};
     setting[key] = defaultValue;
     window.navigator.mozSettings.createLock().set(setting);
   }
   // Figure out the right setter function for this type of pref.
   let setPref;
   switch (typeof defaultValue) {
     case 'boolean':
       setPref = prefs.setBoolPref.bind(prefs);
       break;
     case 'number':
       setPref = prefs.setIntPref.bind(prefs);
       break;
     case 'string':
       setPref = prefs.setCharPref.bind(prefs);
       break;
   }
   SettingsListener.observe(key, defaultValue, function(value) {
     setPref(prefName, value);
   });
 };