Fixes from polymer.dart API review

pkg/polymer/test/template_distribute_dynamic_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:polymer/polymer.dart';
-import 'package:polymer/platform.dart' as Platform;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_config.dart';
 
 @CustomTag('x-test')
 class XTest extends PolymerElement {
   @observable List list;
 
   final _enteredView = new Completer();
   Future onTestDone;
 
   XTest.created() : super.created() {
     onTestDone = _enteredView.future.then(_runTest);
   }
 
   enteredView() {
     super.enteredView();
     _enteredView.complete();
   }
 
   _runTest(_) {
     list = [
       {'name': 'foo'},
       {'name': 'bar'}
     ];
-
-    Platform.flush();
-    Platform.endOfMicrotask(expectAsync0(() {
+    return new Future(() {
       // tickle SD polyfill
       offsetHeight;
       var children = this.$['echo'].children;
       expect(children[0].localName, 'template', reason:
           'shadowDOM dynamic distribution via template');
       expect(children[1].text, 'foo', reason:
           'shadowDOM dynamic distribution via template');
       expect(children[2].text, 'bar', reason:
           'shadowDOM dynamic distribution via template');
 
       // TODO(jmesserly): restore this if we get the JS interop capability.
       /*
       if (window.ShadowDOMPolyfill) {
         var actualChildren = this.$.echo.impl.children;
         chai.assert.equal(actualChildren.length, 4,
           'shadowDOMPolyfill distributes expected number of actual children.');
       }
       */
-    }));
+    });
   }
 }
 
 main() {
   initPolymer();
   useHtmlConfiguration();
 
   setUp(() => Polymer.onReady);
 
   test('inserted called', () => query('x-test').onTestDone);
 }