Temporarily expose createObjectUrl/revokeObjectUrl on window.

lib/html/templates/html/dartium/impl_Window.darttemplate

Index: lib/html/templates/html/dartium/impl_Window.darttemplate
diff --git a/lib/html/templates/html/dartium/impl_Window.darttemplate b/lib/html/templates/html/dartium/impl_Window.darttemplate
index b00851677a61d7ee03ad8bcab94c5628d4b4a5a0..fab97f7b8682737a37daebcb1489011c502990ce 100644
--- a/lib/html/templates/html/dartium/impl_Window.darttemplate
+++ b/lib/html/templates/html/dartium/impl_Window.darttemplate
@@ -24,5 +24,10 @@ class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
     localStorage['dart-port:$name'] = JSON.stringify(serialized);
   }
 
+  String createObjectUrl(object) => DOMURL.createObjectURL(object);
+  void revokeObjectUrl(String url) {
+    DOMURL.revokeObjectURL(url);
+  }
+
 $!MEMBERS
 }