Issue 3251 - Simplify messaging from child scripts to parent

lib/contentPolicy.js

Index: lib/contentPolicy.js
===================================================================
--- a/lib/contentPolicy.js
+++ b/lib/contentPolicy.js
@@ -73,26 +73,18 @@ var Policy = exports.Policy =
    * Called on module startup, initializes various exported properties.
    */
   init: function()
   {
     // whitelisted URL schemes
     for (let scheme of Prefs.whitelistschemes.toLowerCase().split(" "))
       this.whitelistSchemes.add(scheme);
 
-    let messageManager = Cc["@mozilla.org/parentprocessmessagemanager;1"]
-                           .getService(Ci.nsIMessageListenerManager)
-                           .QueryInterface(Ci.nsIMessageBroadcaster);
-    let handler = (message => this.shouldAllow(message.data));
-    messageManager.addMessageListener("AdblockPlus:ShouldAllow", handler);
-    onShutdown.add(() => messageManager.removeMessageListener("AdblockPlus:ShouldAllow", handler));
-
-    let handler2 = () => collapsedClass;
-    messageManager.addMessageListener("AdblockPlus:GetCollapsedClass", handler2);
-    onShutdown.add(() => messageManager.removeMessageListener("AdblockPlus:GetCollapsedClass", handler2));
+    Utils.addChildMessageListener("AdblockPlus:ShouldAllow", this.shouldAllow.bind(this));
+    Utils.addChildMessageListener("AdblockPlus:GetCollapsedClass", () => collapsedClass);
 
     // Generate class identifier used to collapse node and register corresponding
     // stylesheet.
     let offset = "a".charCodeAt(0);
     for (let i = 0; i < 20; i++)
       collapsedClass +=  String.fromCharCode(offset + Math.random() * 26);
 
     let collapseStyle = Services.io.newURI("data:text/css," +