Use Timer and not AnimationFrame during Observatory UI tests

runtime/observatory/tests/observatory_ui/nav/bar/element_test.dart

 // Copyright (c) 2016, 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:html';
 import 'package:unittest/unittest.dart';
+import 'package:observatory/src/elements/helpers/rendering_queue.dart';
 import 'package:observatory/src/elements/nav/bar.dart';
 
 main() {
   NavBarElement.tag.ensureRegistration();
 
+  final TimedRenderingBarrier barrier = new TimedRenderingBarrier();
+  final RenderingQueue queue = new RenderingQueue.fromBarrier(barrier);
   test('instantiation', () {
     final NavBarElement e = new NavBarElement();
     expect(e, isNotNull, reason: 'element correctly created');
   });
   test('elements created', () async {
-    final NavBarElement e = new NavBarElement();
+    final NavBarElement e = new NavBarElement(queue: queue);
     document.body.append(e);
     await e.onRendered.first;
     expect(e.shadowRoot.children.length, isNonZero, reason: 'has elements');
     expect(e.shadowRoot.querySelector('content'), isNotNull,
                                                reason: 'has content elements');
     e.remove();
     await e.onRendered.first;
     expect(e.shadowRoot.children.length, isZero, reason: 'is empty');
   });
 }