Use Timer and not AnimationFrame during Observatory UI tests

runtime/observatory/tests/observatory_ui/nav/top-menu/element_test.dart

Index: runtime/observatory/tests/observatory_ui/nav/top-menu/element_test.dart
diff --git a/runtime/observatory/tests/observatory_ui/nav/top-menu/element_test.dart b/runtime/observatory/tests/observatory_ui/nav/top-menu/element_test.dart
index df9f88c938fc0b8074133c9ed8c3e929751dd807..8d6e8e766de26772fd30320ceaf8e95d07d95036 100644
--- a/runtime/observatory/tests/observatory_ui/nav/top-menu/element_test.dart
+++ b/runtime/observatory/tests/observatory_ui/nav/top-menu/element_test.dart
@@ -3,6 +3,7 @@
 // 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/menu.dart';
 import 'package:observatory/src/elements/nav/top_menu.dart';
 
@@ -11,6 +12,8 @@ main() {
 
   final String tag = NavMenuElement.tag.name;
 
+  final TimedRenderingBarrier barrier = new TimedRenderingBarrier();
+  final RenderingQueue queue = new RenderingQueue.fromBarrier(barrier);
   group('instantiation', () {
     test('default', () {
       final NavTopMenuElement e = new NavTopMenuElement();
@@ -29,7 +32,7 @@ main() {
   });
   group('elements', () {
     test('created', () async {
-      final NavTopMenuElement e = new NavTopMenuElement();
+      final NavTopMenuElement e = new NavTopMenuElement(queue: queue);
       document.body.append(e);
       await e.onRendered.first;
       expect(e.shadowRoot.children.length, isNonZero, reason: 'has elements');
@@ -40,7 +43,8 @@ main() {
       expect(e.shadowRoot.children.length, isZero, reason: 'is empty');
     });
     test('react to last change', () async {
-      final NavTopMenuElement e = new NavTopMenuElement(last: false);
+      final NavTopMenuElement e = new NavTopMenuElement(last: false,
+          queue: queue);
       document.body.append(e);
       await e.onRendered.first;
       expect((e.shadowRoot.querySelector(tag) as NavMenuElement).last, isFalse);