Bringing dart:html's spawnDomFunction into sync between dart2js and dartium.

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 9c9645af31d2d4642b031e922f513f4322cd52c4..f179a1607536fce4ad3f235eacd35b98287843ec 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -65,7 +65,8 @@ _callPortSync(int id, message) {
   return JS('var', r'ReceivePortSync.dispatchCall(#, #)', id, message);
 }
 
-spawnDomFunction(Function f) => IsolateNatives.spawnDomFunction(f);
+Future<SendPort> spawnDomFunction(Function f) =>
+  new Future.value(IsolateNatives.spawnDomFunction(f));
 // 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.