Fixes from polymer.dart API review

pkg/polymer/test/bind_mdv_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 polymer.test.bind_mdv_test;
 
 import 'dart:async';
 import 'dart:html';
 import 'package:custom_element/polyfill.dart';
 import 'package:template_binding/template_binding.dart';
 import 'package:observe/observe.dart';
-import 'package:observe/src/microtask.dart' show runMicrotask;
-import 'package:polymer/platform.dart' as Platform;
 import 'package:unittest/html_config.dart';
 import 'package:unittest/unittest.dart';
 
 main() {
   useHtmlConfiguration();
 
   var registered = loadCustomElementPolyfill().then((_) {
     document.register('my-div', MyDivElement);
   });
 
@@ skipping 36 matching lines @@
 
   test('bind input', () {
     var fragment = parseAndBindHTML('<input value="{{bar}}" />', div);
     div.append(fragment);
     var a = div.query('input');
 
     div.bar = 'hello';
     // TODO(sorvell): fix this when observe-js lets us explicitly listen for
     // a change on input.value
     Observable.dirtyCheck();
-    Platform.endOfMicrotask(expectAsync0(() {
+    return new Future.microtask(() {
       expect(a.value, 'hello');
-    }));
+    });
   });
 }
 
 class MyDivElement extends HtmlElement with Observable {
   factory MyDivElement() => new Element.tag('my-div');
   MyDivElement.created() : super.created();
   @observable var bar;
 }
 
 class NullTreeSanitizer implements NodeTreeSanitizer {
   const NullTreeSanitizer();
   void sanitizeTree(Node node) {}
 }
 
 Future onAttributeChange(Element node) {
   var completer = new Completer();
   new MutationObserver((records, observer) {
     observer.disconnect();
     completer.complete();
   })..observe(node, attributes: true);
-  Platform.flush();
+  scheduleMicrotask(Observable.dirtyCheck);
   return completer.future;
-}
+}