Safely wrap window.top in frog dom.

client/dom/templates/dom/frog/impl_DOMWindow.darttemplate

Index: client/dom/templates/dom/frog/impl_DOMWindow.darttemplate
diff --git a/client/dom/templates/dom/frog/impl_DOMWindow.darttemplate b/client/dom/templates/dom/frog/impl_DOMWindow.darttemplate
new file mode 100644
index 0000000000000000000000000000000000000000..14f8d9a7aea19978140a12f97bd33419aba53186
--- /dev/null
+++ b/client/dom/templates/dom/frog/impl_DOMWindow.darttemplate
@@ -0,0 +1,12 @@
+// 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 _top() native "return this.top;";
+
+  // Override top to return secure wrapper.
+  Window get top() => _DOMWindowCrossFrameImpl._createSafe(_top);
+}