Work-around Frog codegen bug where Window is derived from native DOMWindow.

client/dom/scripts/template_frog_dom.darttemplate

Index: client/dom/scripts/template_frog_dom.darttemplate
diff --git a/client/dom/scripts/template_frog_dom.darttemplate b/client/dom/scripts/template_frog_dom.darttemplate
index 4895350c2be11e4fdbd7b7c59dc6c9fbb7b1d60d..241baad60d90c4b9f1a3048ace1476f1ba164e70 100644
--- a/client/dom/scripts/template_frog_dom.darttemplate
+++ b/client/dom/scripts/template_frog_dom.darttemplate
@@ -17,7 +17,10 @@ $!GENERATED_DART_FILES
 #source('src/_ListIterators.dart');
 #source('src/_Lists.dart');
 
-class Window extends DOMWindow {}
+// TODO(jmesserly): 'native' here is aWork-around for Frog bug.  Frog needs to
+// be smarter about inheriting from a hidden native type (in this case
+// DOMWindow)
+class Window extends DOMWindow native "*Window" {}
 DOMWindow get window() native "return window;";
 // TODO(vsm): Revert to Dart method when 508 is fixed.
 HTMLDocument get document() native "return window.document;";