fix forceReady test in IE

pkg/polymer/test/force_ready_test.dart

 // Copyright (c) 2013, 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.
 
 import 'dart:async';
 import 'dart:html';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import 'package:polymer/polymer.dart';
 
 main() => initPolymer().run(() {
   useHtmlConfiguration();
 
   setUp(() => window.on['HTMLImportsLoaded']);
 
   /// We do not port the full test, since this just proxies through to the
   /// polymer js implementation.
   test('can force ready', () {
-    expect(Polymer.waitingFor.length, 1);
-    expect(Polymer.waitingFor[0], querySelector('polymer-element'));
-    Polymer.forceReady();
-    return Polymer.onReady;
+    return new Future(() {}).then((_) {
+      expect(Polymer.waitingFor.length, 1);
+      expect(Polymer.waitingFor[0], querySelector('polymer-element'));
+      Polymer.forceReady();
+      return Polymer.onReady;
+    });
   });
 });