Wrap Window in case it's a window from a different page / frame.

lib/html/templates/html/dart2js/impl_IFrameElement.darttemplate

Index: lib/html/templates/html/dart2js/impl_IFrameElement.darttemplate
diff --git a/lib/html/templates/html/dart2js/impl_IFrameElement.darttemplate b/lib/html/templates/html/dart2js/impl_IFrameElement.darttemplate
deleted file mode 100644
index 5f91ec8526b603ca0f668c5b44fca66afe7f3161..0000000000000000000000000000000000000000
--- a/lib/html/templates/html/dart2js/impl_IFrameElement.darttemplate
+++ /dev/null
@@ -1,14 +0,0 @@
-// 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
-
-  Window get _contentWindow() native "return this.contentWindow;";
-
-  // Override contentWindow to return secure wrapper.
-  Window get contentWindow {
-    return _DOMWindowCrossFrameImpl._createSafe(_contentWindow);
-  }
-}