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

lib/dom/templates/html/frog/impl_Window.darttemplate

Index: lib/dom/templates/html/frog/impl_Window.darttemplate
diff --git a/lib/dom/templates/html/frog/impl_Window.darttemplate b/lib/dom/templates/html/frog/impl_Window.darttemplate
index 746e5921b9942d51f2d7496ff72eae38229d65ad..78335ee8d057cfc33755ccefcb7eb6afed36cd74 100644
--- a/lib/dom/templates/html/frog/impl_Window.darttemplate
+++ b/lib/dom/templates/html/frog/impl_Window.darttemplate
@@ -6,6 +6,11 @@ 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);
   }