Use Timer and not AnimationFrame during Observatory UI tests

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

Index: runtime/observatory/tests/observatory_ui/nav/bar/element_test.dart
diff --git a/runtime/observatory/tests/observatory_ui/nav/bar/element_test.dart b/runtime/observatory/tests/observatory_ui/nav/bar/element_test.dart
index fe547857a42a4f11ec601d27ce1dc0d96b941e11..98b4f5abaa548b1639846b31636a687407e7b930 100644
--- a/runtime/observatory/tests/observatory_ui/nav/bar/element_test.dart
+++ b/runtime/observatory/tests/observatory_ui/nav/bar/element_test.dart
@@ -3,17 +3,20 @@
 // 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');