diff -r 000000000000 -r 6474c204b198 b2g/chrome/content/screen.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/b2g/chrome/content/screen.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,258 @@
+// screen.js:
+// Set the screen size, pixel density and scaling of the b2g client screen
+// based on the --screen command-line option, if there is one.
+// 
+// TODO: support multiple device pixels per CSS pixel
+// 
+
+// We do this on ContentStart because querying the displayDPI fails otherwise.
+window.addEventListener('ContentStart', function() {
+  // This is the toplevel <window> element
+  let shell = document.getElementById('shell');
+
+  // The <browser> element inside it
+  let browser = document.getElementById('systemapp');
+
+  // Figure out the native resolution of the screen
+  let windowUtils = window.QueryInterface(Ci.nsIInterfaceRequestor)
+    .getInterface(Components.interfaces.nsIDOMWindowUtils);
+  let hostDPI = windowUtils.displayDPI;
+
+  let DEFAULT_SCREEN = '320x480';
+
+  // This is a somewhat random selection of named screens.
+  // Add more to this list when we support more hardware.
+  // Data from: http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density
+  let screens = {
+    iphone: {
+      name: 'Apple iPhone', width:320, height:480,  dpi:163
+    },
+    ipad: {
+      name: 'Apple iPad', width:1024, height:768,  dpi:132
+    },
+    nexus_s: {
+      name: 'Samsung Nexus S', width:480, height:800, dpi:235
+    },
+    galaxy_s2: {
+      name: 'Samsung Galaxy SII (I9100)', width:480, height:800, dpi:219
+    },
+    galaxy_nexus: {
+      name: 'Samsung Galaxy Nexus', width:720, height:1280, dpi:316
+    },
+    galaxy_tab: {
+      name: 'Samsung Galaxy Tab 10.1', width:800, height:1280, dpi:149
+    },
+    wildfire: {
+      name: 'HTC Wildfire', width:240, height:320, dpi:125
+    },
+    tattoo: {
+      name: 'HTC Tattoo', width:240, height:320, dpi:143
+    },
+    salsa: {
+      name: 'HTC Salsa', width:320, height:480, dpi:170
+    },
+    chacha: {
+      name: 'HTC ChaCha', width:320, height:480, dpi:222
+    },
+  };
+
+  // Get the command line arguments that were passed to the b2g client
+  let args;
+  try {
+    // On Firefox Mulet, we don't always have a command line argument
+    args = window.arguments[0].QueryInterface(Ci.nsICommandLine);
+  } catch(e) {}
+
+  let screenarg = null;
+
+  // Get the --screen argument from the command line
+  try {
+    if (args) {
+      screenarg = args.handleFlagWithParam('screen', false);
+    }
+
+    // If there isn't one, use the default screen
+    if (screenarg === null)
+      screenarg = DEFAULT_SCREEN;
+
+    // With no value, tell the user how to use it
+    if (screenarg == '')
+      usage();
+  }
+  catch(e) {
+    // If getting the argument value fails, its an error
+    usage();
+  }
+  
+  // Special case --screen=full goes into fullscreen mode
+  if (screenarg === 'full') {
+    shell.setAttribute('sizemode', 'fullscreen');
+    return;
+  } 
+
+  let rescale = false;
+
+  // If the value of --screen ends with !, we'll be scaling the output
+  if (screenarg[screenarg.length - 1] === '!') {
+    rescale = true;
+    screenarg = screenarg.substring(0, screenarg.length-1);
+  }
+
+  let width, height, dpi;
+
+  if (screenarg in screens) {
+    // If this is a named screen, get its data
+    let screen = screens[screenarg];
+    width = screen.width;
+    height = screen.height;
+    dpi = screen.dpi;
+  } else {
+    // Otherwise, parse the resolution and density from the --screen value.
+    // The supported syntax is WIDTHxHEIGHT[@DPI]
+    let match = screenarg.match(/^(\d+)x(\d+)(@(\d+))?$/);
+    
+    // Display usage information on syntax errors
+    if (match == null)
+      usage();
+    
+    // Convert strings to integers
+    width = parseInt(match[1], 10);
+    height = parseInt(match[2], 10);
+    if (match[4])
+      dpi = parseInt(match[4], 10);
+    else    // If no DPI, use the actual dpi of the host screen
+      dpi = hostDPI;
+
+    // If any of the values came out 0 or NaN or undefined, display usage
+    if (!width || !height || !dpi)
+      usage();
+  }
+
+  Cu.import("resource://gre/modules/GlobalSimulatorScreen.jsm");
+  function resize(width, height, dpi, shouldFlip) {
+    GlobalSimulatorScreen.width = width;
+    GlobalSimulatorScreen.height = height;
+
+    // In order to do rescaling, we set the <browser> tag to the specified
+    // width and height, and then use a CSS transform to scale it so that
+    // it appears at the correct size on the host display.  We also set
+    // the size of the <window> element to that scaled target size.
+    let scale = rescale ? hostDPI / dpi : 1;
+
+    // Set the window width and height to desired size plus chrome
+    // Include the size of the toolbox displayed under the system app
+    let controls = document.getElementById('controls');
+    let controlsHeight = 0;
+    if (controls) {
+      controlsHeight = controls.getBoundingClientRect().height;
+    }
+    let chromewidth = window.outerWidth - window.innerWidth;
+    let chromeheight = window.outerHeight - window.innerHeight + controlsHeight;
+    window.resizeTo(Math.round(width * scale) + chromewidth,
+                    Math.round(height * scale) + chromeheight);
+
+    let frameWidth = width, frameHeight = height;
+    if (shouldFlip) {
+      frameWidth = height;
+      frameHeight = width;
+    }
+
+    // Set the browser element to the full unscaled size of the screen
+    let style = browser.style;
+    style.width = style.minWidth = style.maxWidth =
+      frameWidth + 'px';
+    style.height = style.minHeight = style.maxHeight =
+      frameHeight + 'px';
+    browser.setAttribute('flex', '0');  // Don't let it stretch
+
+    style.transformOrigin = '';
+    style.transform = '';
+
+    // Now scale the browser element as needed
+    if (scale !== 1) {
+      style.transformOrigin = 'top left';
+      style.transform += ' scale(' + scale + ',' + scale + ')';
+    }
+
+    if (shouldFlip) {
+      // Display the system app with a 90° clockwise rotation
+      let shift = Math.floor(Math.abs(frameWidth-frameHeight) / 2);
+      style.transform +=
+        ' rotate(0.25turn) translate(-' + shift + 'px, -' + shift + 'px)';
+    }
+
+    // Set the pixel density that we want to simulate.
+    // This doesn't change the on-screen size, but makes
+    // CSS media queries and mozmm units work right.
+    Services.prefs.setIntPref('layout.css.dpi', dpi);
+  }
+
+  // Resize on startup
+  resize(width, height, dpi, false);
+
+  let defaultOrientation = width < height ? 'portrait' : 'landscape';
+
+  // Then resize on each rotation button click,
+  // or when the system app lock/unlock the orientation
+  Services.obs.addObserver(function orientationChangeListener(subject) {
+    let screen = subject.wrappedJSObject;
+    let { mozOrientation, screenOrientation } = screen;
+
+    let newWidth = width;
+    let newHeight = height;
+    // If we have an orientation different than the startup one,
+    // we switch the sizes
+    if (screenOrientation != defaultOrientation) {
+      newWidth = height;
+      newHeight = width;
+    }
+
+    // If the current app doesn't supports the current screen orientation
+    // still resize the window, but rotate its frame so that
+    // it is displayed rotated on the side
+    let shouldFlip = mozOrientation != screenOrientation;
+
+    resize(newWidth, newHeight, dpi, shouldFlip);
+  }, 'simulator-adjust-window-size', false);
+
+  // A utility function like console.log() for printing to the terminal window
+  // Uses dump(), but enables it first, if necessary
+  function print() {
+    let dump_enabled =
+      Services.prefs.getBoolPref('browser.dom.window.dump.enabled');
+
+    if (!dump_enabled)
+      Services.prefs.setBoolPref('browser.dom.window.dump.enabled', true);
+
+    dump(Array.prototype.join.call(arguments, ' ') + '\n');
+
+    if (!dump_enabled) 
+      Services.prefs.setBoolPref('browser.dom.window.dump.enabled', false);
+  }
+
+  // Print usage info for --screen and exit
+  function usage() {
+    // Documentation for the --screen argument
+    let msg = 
+      'The --screen argument specifies the desired resolution and\n' +
+      'pixel density of the simulated device screen. Use it like this:\n' +
+      '\t--screen=WIDTHxHEIGHT\t\t\t// E.g.: --screen=320x480\n' +
+      '\t--screen=WIDTHxHEIGHT@DOTS_PER_INCH\t// E.g.: --screen=480x800@250\n' +
+      '\t--screen=full\t\t\t\t// run in fullscreen mode\n' +
+      '\nYou can also specify certain device names:\n';
+    for(let p in screens)
+      msg += '\t--screen=' + p + '\t// ' + screens[p].name + '\n';
+    msg += 
+      '\nAdd a ! to the end of a screen specification to rescale the\n' +
+      'screen so that it is shown at actual size on your monitor:\n' +
+      '\t--screen=nexus_s!\n' +
+      '\t--screen=320x480@200!\n'
+    ;
+
+    // Display the usage message
+    print(msg);
+
+    // Exit the b2g client
+    Services.startup.quit(Ci.nsIAppStartup.eAttemptQuit);
+  }
+});