Fix SendPortSync dispatch for FF

lib/html/templates/html/dartium/html_dartium.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // DO NOT EDIT
 // Auto-generated dart:html library.
 
 #library("dart:html");
 
 #import("dart:isolate");
@@ skipping 51 matching lines @@
 ElementList queryAll(String selector) => _document.queryAll(selector);
 
 int _getNewIsolateId() => _Utils._getNewIsolateId();
 
 bool _callPortInitialized = false;
 var _callPortLastResult = null;
 
 _callPortSync(num id, var message) {
   if (!_callPortInitialized) {
     window.on['js-result'].add((event) {
-      _callPortLastResult = JSON.parse(event.data);
+      _callPortLastResult = JSON.parse(_getPortSyncEventData(event));
     }, false);
     _callPortInitialized = true;
   }
   assert(_callPortLastResult == null);
   _dispatchEvent('js-sync-message', {'id': id, 'message': message});
   var result = _callPortLastResult;
   _callPortLastResult = null;
   return result;
 }