Bugfix in html_dart2js: Detect window objects in a way compatible with cross domain iframes

dart/tools/dom/src/dart2js_Conversions.dart

 // 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.
 
 
 // Conversions for Window.  These check if the window is the local
 // window, and if it's not, wraps or unwraps it with a secure wrapper.
 // We need to test for EventTarget here as well as it's a base type.
 // We omit an unwrapper for Window as no methods take a non-local
 // window as a parameter.
 
 part of html;
 
 WindowBase _convertNativeToDart_Window(win) {
   if (win == null) return null;
   return _DOMWindowCrossFrame._createSafe(win);
 }
 
 EventTarget _convertNativeToDart_EventTarget(e) {
   if (e == null) {
     return null;
   }
-  // Assume it's a Window if it contains the setInterval property.  It may be
+  // Assume it's a Window if it contains the postMessage property.  It may be
   // from a different frame - without a patched prototype - so we cannot
   // rely on Dart type checking.
-  if (JS('bool', r'"setInterval" in #', e)) {
+  if (JS('bool', r'"postMessage" in #', e)) {
     var window = _DOMWindowCrossFrame._createSafe(e);
     // If it's a native window.
     if (window is EventTarget) {
       return window;
     }
     return null;
   }
   else
     return e;
 }
 
 EventTarget _convertDartToNative_EventTarget(e) {
   if (e is _DOMWindowCrossFrame) {
     return e._window;
   } else {
     return e;
   }
 }
 
 _convertNativeToDart_XHR_Response(o) {
   if (o is Document) {
     return o;
   }
   return convertNativeToDart_SerializedScriptValue(o);
 }