Fixes from polymer.dart API review

samples/third_party/todomvc/test/markdone_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.
 
 library todomvc.test.markdone_test;
 
 import 'dart:async';
 import 'dart:html';
-import 'package:polymer/platform.dart' show endOfMicrotask;
 import 'package:polymer/polymer.dart';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 import '../web/model.dart';
 
 Node findWithText(Node node, String text) {
   if (node.text == text) return node;
   if (node is Element && (node as Element).localName == 'polymer-element') {
     return null;
   }
@@ skipping 33 matching lines @@
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('mark done', () {
     appModel.todos.add(new Todo('one (unchecked)'));
     appModel.todos.add(new Todo('two (unchecked)'));
     appModel.todos.add(new Todo('three (checked)')..done = true);
     appModel.todos.add(new Todo('four (checked)'));
 
-    endOfMicrotask(expectAsync0(() {
+    return new Future(() {
       var body = query('body');
 
       var label = findWithText(body, 'four (checked)');
       expect(label is LabelElement, true, reason: 'text is in a label: $label');
 
       var host = findShadowHost(body, label.parentNode);
       var node = host.parent.query('input');
       expect(node is InputElement, true, reason: 'node is a checkbox');
       expect(node.type, 'checkbox', reason: 'node type is checkbox');
       expect(node.checked, isFalse, reason: 'element is unchecked');
 
       node.dispatchEvent(new MouseEvent('click', detail: 1));
       expect(node.checked, true, reason: 'element is checked');
-    }));
+    });
   });
 }