Minimal fix to get cross frame tests working.

lib/dom/templates/html/frog/impl_Window.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.
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS native "@*DOMWindow" {
 
   _DocumentImpl get document() native "return this.document;";
 
+  Window get _top() native "return this.top;";
+
+  // Override top to return secure wrapper.
+  Window get top() => _DOMWindowCrossFrameImpl._createSafe(_top);
+
   void requestLayoutFrame(TimeoutHandler callback) {
     _addMeasurementFrameCallback(callback);
   }
 
   /** @domName DOMWindow.requestAnimationFrame */
   int requestAnimationFrame(RequestAnimationFrameCallback callback) native '''
     if (!window.requestAnimationFrame) {
       window.requestAnimationFrame =
           window.webkitRequestAnimationFrame ||
           window.mozRequestAnimationFrame ||
           window.msRequestAnimationFrame ||
           window.oRequestAnimationFrame ||
           function (callback) {
             window.setTimeout(callback, 16 /* 16ms ~= 60fps */);
           };
     }
     return window.requestAnimationFrame(callback);
 ''';
 
   // Protect member 'requestAnimationFrame'.
   _requestAnimationFrame() native 'requestAnimationFrame';
 
 $!MEMBERS
 }