Simplified and removed memory leaks from code dealing with frames on Chrome

webrequest.js

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2014 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 58 matching lines @@
 {
   function onHeadersReceived(details)
   {
     if (details.tabId == -1)
       return;
 
     if (details.type != "main_frame" && details.type != "sub_frame")
       return;
 
     var page = new ext.Page({id: details.tabId});
-    var frame = new ext.Frame({frameId: details.frameId, tabId: details.tabId});
+    var frame = ext.getFrame(details.tabId, details.frameId);
 
-    if (frame.url != details.url)
+    if (!frame || frame.url != details.url)
       return;
 
     for (var i = 0; i < details.responseHeaders.length; i++)
     {
       var header = details.responseHeaders[i];
       if (header.name.toLowerCase() == "x-adblock-key" && header.value)
         processKeyException(header.value, page, frame);
     }
   }
 
   chrome.webRequest.onHeadersReceived.addListener(onHeadersReceived, {urls: ["<all_urls>"]}, ["responseHeaders"]);
 }