diff -r 000000000000 -r 6474c204b198 dom/datastore/DataStoreChangeNotifier.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/datastore/DataStoreChangeNotifier.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,132 @@
+/* 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, results: Cr} = Components;
+
+this.EXPORTED_SYMBOLS = ["DataStoreChangeNotifier"];
+
+function debug(s) {
+  //dump('DEBUG DataStoreChangeNotifier: ' + s + '\n');
+}
+
+// DataStoreServiceInternal should not be converted into a lazy getter as it
+// runs code during initialization.
+Cu.import('resource://gre/modules/DataStoreServiceInternal.jsm');
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
+
+XPCOMUtils.defineLazyServiceGetter(this, "ppmm",
+                                   "@mozilla.org/parentprocessmessagemanager;1",
+                                   "nsIMessageBroadcaster");
+
+this.DataStoreChangeNotifier = {
+  children: [],
+  messages: [ "DataStore:Changed", "DataStore:RegisterForMessages",
+              "DataStore:UnregisterForMessages",
+              "child-process-shutdown" ],
+
+  init: function() {
+    debug("init");
+
+    this.messages.forEach((function(msgName) {
+      ppmm.addMessageListener(msgName, this);
+    }).bind(this));
+
+    Services.obs.addObserver(this, 'xpcom-shutdown', false);
+  },
+
+  observe: function(aSubject, aTopic, aData) {
+    debug("observe");
+
+    switch (aTopic) {
+      case 'xpcom-shutdown':
+        this.messages.forEach((function(msgName) {
+          ppmm.removeMessageListener(msgName, this);
+        }).bind(this));
+
+        Services.obs.removeObserver(this, 'xpcom-shutdown');
+        ppmm = null;
+        break;
+
+      default:
+        debug("Wrong observer topic: " + aTopic);
+        break;
+    }
+  },
+
+  broadcastMessage: function broadcastMessage(aData) {
+    debug("Broadast");
+    this.children.forEach(function(obj) {
+      if (obj.store == aData.store && obj.owner == aData.owner) {
+        obj.mm.sendAsyncMessage("DataStore:Changed:Return:OK", aData);
+      }
+    });
+  },
+
+
+  receiveMessage: function(aMessage) {
+    debug("receiveMessage");
+
+    // No check has to be done when the message is 'child-process-shutdown'
+    // because at this point the target is already disconnected from
+    // nsFrameMessageManager, so that assertAppHasStatus will always fail.
+    let prefName = 'dom.testing.datastore_enabled_for_hosted_apps';
+    if (aMessage.name != 'child-process-shutdown' &&
+        (Services.prefs.getPrefType(prefName) == Services.prefs.PREF_INVALID ||
+         !Services.prefs.getBoolPref(prefName)) &&
+        !aMessage.target.assertAppHasStatus(Ci.nsIPrincipal.APP_STATUS_CERTIFIED)) {
+      return;
+    }
+
+    switch (aMessage.name) {
+      case "DataStore:Changed":
+        this.broadcastMessage(aMessage.data);
+        break;
+
+      case "DataStore:RegisterForMessages":
+        debug("Register!");
+
+        for (let i = 0; i < this.children.length; ++i) {
+          if (this.children[i].mm == aMessage.target &&
+              this.children[i].store == aMessage.data.store &&
+              this.children[i].owner == aMessage.data.owner) {
+            debug("Register on existing index: " + i);
+            ++this.children[i].count;
+            return;
+          }
+        }
+
+        this.children.push({ mm: aMessage.target,
+                             store: aMessage.data.store,
+                             owner: aMessage.data.owner,
+                             count: 1 });
+        break;
+
+      case "child-process-shutdown":
+      case "DataStore:UnregisterForMessages":
+        debug("Unregister");
+
+        for (let i = 0; i < this.children.length;) {
+          if (this.children[i].mm == aMessage.target) {
+            debug("Unregister index: " + i);
+            if (!--this.children[i].count) {
+              debug("Unregister delete index: " + i);
+              this.children.splice(i, 1);
+            }
+            break;
+          } else {
+            ++i;
+          }
+        }
+        break;
+
+      default:
+        debug("Wrong message: " + aMessage.name);
+    }
+  }
+}
+
+DataStoreChangeNotifier.init();