Minimal fix to get cross frame tests working, take #2.

lib/dom/templates/html/frog/impl_IFrameElement.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$IMPLEMENTS$NATIVESPEC {
+$!MEMBERS
 
-  _DocumentImpl get document() => _wrap(_ptr.document);
+  Window get _contentWindow() native "return this.contentWindow;";
 
-  void requestLayoutFrame(TimeoutHandler callback) {
-    _addMeasurementFrameCallback(callback);
+  // Override contentWindow to return secure wrapper.
+  Window get contentWindow() {
+    return _DOMWindowCrossFrameImpl._createSafe(_contentWindow);
   }
-
-  int requestAnimationFrame(RequestAnimationFrameCallback callback) =>
-      webkitRequestAnimationFrame(callback);
-
-$!MEMBERS
 }