diff -r 000000000000 -r 6474c204b198 b2g/components/SystemAppProxy.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/b2g/components/SystemAppProxy.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,114 @@
+/* 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 { classes: Cc, interfaces: Ci, utils: Cu } = Components;
+
+Cu.import('resource://gre/modules/XPCOMUtils.jsm');
+Cu.import('resource://gre/modules/Services.jsm');
+
+this.EXPORTED_SYMBOLS = ['SystemAppProxy'];
+
+let SystemAppProxy = {
+  _frame: null,
+  _isReady: false,
+  _pendingEvents: [],
+  _pendingListeners: [],
+
+  // To call when a new system app iframe is created
+  registerFrame: function (frame) {
+    this._isReady = false;
+    this._frame = frame;
+
+    // Register all DOM event listeners added before we got a ref to the app iframe
+    this._pendingListeners
+        .forEach((args) =>
+                 this.addEventListener.apply(this, args));
+    this._pendingListeners = [];
+  },
+
+  // To call when it is ready to receive events
+  setIsReady: function () {
+    if (this._isReady) {
+      Cu.reportError('SystemApp has already been declared as being ready.');
+    }
+    this._isReady = true;
+
+    // Dispatch all events being queued while the system app was still loading
+    this._pendingEvents
+        .forEach(([type, details]) =>
+                 this._sendCustomEvent(type, details));
+    this._pendingEvents = [];
+  },
+
+  /*
+   * Common way to send an event to the system app.
+   *
+   * // In gecko code:
+   *   SystemAppProxy.sendCustomEvent('foo', { data: 'bar' });
+   * // In system app:
+   *   window.addEventListener('foo', function (event) {
+   *     event.details == 'bar'
+   *   });
+   */
+  _sendCustomEvent: function systemApp_sendCustomEvent(type, details) {
+    let content = this._frame ? this._frame.contentWindow : null;
+
+    // If the system app isn't ready yet,
+    // queue events until someone calls setIsLoaded
+    if (!this._isReady || !content) {
+      this._pendingEvents.push([type, details]);
+      return null;
+    }
+
+    let event = content.document.createEvent('CustomEvent');
+
+    let payload;
+    // If the root object already has __exposedProps__,
+    // we consider the caller already wrapped (correctly) the object.
+    if ('__exposedProps__' in details) {
+      payload = details;
+    } else {
+      payload = details ? Cu.cloneInto(details, content) : {};
+    }
+
+    event.initCustomEvent(type, true, false, payload);
+    content.dispatchEvent(event);
+
+    return event;
+  },
+
+  // Now deprecated, use sendCustomEvent with a custom event name
+  dispatchEvent: function systemApp_sendChromeEvent(details) {
+    return this._sendCustomEvent('mozChromeEvent', details);
+  },
+
+  // Listen for dom events on the system app
+  addEventListener: function systemApp_addEventListener() {
+    let content = this._frame ? this._frame.contentWindow : null;
+    if (!content) {
+      this._pendingListeners.push(arguments);
+      return false;
+    }
+
+    content.addEventListener.apply(content, arguments);
+    return true;
+  },
+
+  removeEventListener: function systemApp_removeEventListener(name, listener) {
+    let content = this._frame ? this._frame.contentWindow : null;
+    if (content) {
+      content.removeEventListener.apply(content, arguments);
+    } else {
+      let idx = this._pendingListeners.indexOf(listener);
+      if (idx != -1) {
+        this._pendingListeners.splice(idx, 1);
+      }
+    }
+  }
+
+};
+this.SystemAppProxy = SystemAppProxy;
+