Issue 1663 - Emulate background page and implement proper message responder

ext/common.js

Index: ext/common.js
===================================================================
--- a/ext/common.js
+++ b/ext/common.js
@@ -12,16 +12,62 @@
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 (function(global)
 {
+  if (!global.ext)
+    global.ext = {};
+
+  /* Message passing */
+
+  global.ext.onMessage =
+  {
+    addListener: function(listener)
+    {
+      listener.__wrapper = function(event)
+      {
+        if (event.data.type != "message")
+          return;
+
+        var message = event.data.payload;
+        var messageId = event.data.messageId;
+        var sender = {
+          sendMessage: function(message)
+          {
+            event.source.postMessage({
+              type: "message",
+              messageId: -1,
+              payload: message
+            }, "*");
+          }
+        };
+        var callback = function(message)
+        {
+          event.source.postMessage({
+            type: "response",
+            messageId: messageId,
+            payload: message
+          }, "*");
+        };
+        listener(message, sender, callback);
+      };
+      window.addEventListener("message", listener.__wrapper, false);
+    },
+
+    removeListener: function(listener)
+    {
+      if ("__wrapper" in listener)
+        window.removeEventListener("message", listener.__wrapper, false);
+    }
+  };
+
   /* I18n */
 
   var getLocaleCandidates = function(selectedLocale)
   {
     var candidates = [];
     var defaultLocale = "en-US";
 
     // e.g. "ja-jp-mac" -> "ja-JP", note that the part after the second
@@ -105,19 +151,16 @@
     var rawCatalog = JSON.parse(xhr.responseText);
     for (var msgId in rawCatalog)
     {
       if (!(msgId in catalog))
         catalog[msgId] = parseMessage(rawCatalog[msgId]);
     }
   };
 
-  if (!global.ext)
-    global.ext = {};
-
   global.ext.i18n = {
     getMessage: function(msgId, substitutions)
     {
       while (true)
       {
         var message = catalog[msgId];
         if (message)
         {