Use Timer and not AnimationFrame during Observatory UI tests

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

Index: runtime/observatory/tests/observatory_ui/nav/class-menu/element_test.dart
diff --git a/runtime/observatory/tests/observatory_ui/nav/class-menu/element_test.dart b/runtime/observatory/tests/observatory_ui/nav/class-menu/element_test.dart
index df83ea482787580effac6bf8ac7b31f3af2a2ef8..5ed76a3c89b7b7b4a153c17a26249605aa992485 100644
--- a/runtime/observatory/tests/observatory_ui/nav/class-menu/element_test.dart
+++ b/runtime/observatory/tests/observatory_ui/nav/class-menu/element_test.dart
@@ -4,11 +4,15 @@
 import 'dart:html';
 import 'package:unittest/unittest.dart';
 import 'package:observatory/mocks.dart';
+import 'package:observatory/src/elements/helpers/rendering_queue.dart';
 import 'package:observatory/src/elements/nav/class_menu.dart';
 
 main(){
   NavClassMenuElement.tag.ensureRegistration();
 
+  final TimedRenderingBarrier barrier = new TimedRenderingBarrier();
+  final RenderingQueue queue = new RenderingQueue.fromBarrier(barrier);
+
   final IsolateRefMock i_ref = const IsolateRefMock(id: 'i-id', name: 'i-name');
   final ClassRefMock c_ref = const ClassRefMock(id: 'c-id', name: 'c-name');
   test('instantiation', () {
@@ -18,7 +22,8 @@ main(){
     expect(e.cls, equals(c_ref));
   });
   test('elements created after attachment', () async {
-    final NavClassMenuElement e = new NavClassMenuElement(i_ref, c_ref);
+    final NavClassMenuElement e = new NavClassMenuElement(i_ref, c_ref,
+        queue: queue);
     document.body.append(e);
     await e.onRendered.first;
     expect(e.shadowRoot.children.length, isNonZero, reason: 'has elements');