Use Timer and not AnimationFrame during Observatory UI tests

runtime/observatory/tests/observatory_ui/nav/notify_exception/exception_test.dart

Index: runtime/observatory/tests/observatory_ui/nav/notify_exception/exception_test.dart
diff --git a/runtime/observatory/tests/observatory_ui/nav/notify_exception/exception_test.dart b/runtime/observatory/tests/observatory_ui/nav/notify_exception/exception_test.dart
index be9fdc5fdacf638dd5e875ab40ec6c4ef9bfa7a8..74c7e13738279d1300880ce7be15bb79e7da079b 100644
--- a/runtime/observatory/tests/observatory_ui/nav/notify_exception/exception_test.dart
+++ b/runtime/observatory/tests/observatory_ui/nav/notify_exception/exception_test.dart
@@ -4,11 +4,15 @@
 import 'dart:html';
 import 'dart:async';
 import 'package:unittest/unittest.dart';
+import 'package:observatory/src/elements/helpers/rendering_queue.dart';
 import 'package:observatory/src/elements/nav/notify_exception.dart';
 
 main() {
   NavNotifyExceptionElement.tag.ensureRegistration();
 
+  final TimedRenderingBarrier barrier = new TimedRenderingBarrier();
+  final RenderingQueue queue = new RenderingQueue.fromBarrier(barrier);
+
   final StackTrace stacktrace = new StackTrace.fromString('stacktrace string');
   group('normal exception', () {
     final Exception exception = new Exception('exception message');
@@ -31,7 +35,7 @@ main() {
     group('elements', () {
       test('created after attachment (no stacktrace)', () async {
         final NavNotifyExceptionElement e =
-                                      new NavNotifyExceptionElement(exception);
+            new NavNotifyExceptionElement(exception, queue: queue);
         document.body.append(e);
         await e.onRendered.first;
         expect(e.children.length, isNonZero, reason: 'has elements');
@@ -43,7 +47,8 @@ main() {
       });
       test('created after attachment (with stacktrace)', () async {
         final NavNotifyExceptionElement e =
-              new NavNotifyExceptionElement(exception, stacktrace: stacktrace);
+            new NavNotifyExceptionElement(exception, stacktrace: stacktrace,
+            queue: queue);
         document.body.append(e);
         await e.onRendered.first;
         expect(e.children.length, isNonZero, reason: 'has elements');
@@ -58,13 +63,15 @@ main() {
       NavNotifyExceptionElement e;
       StreamSubscription sub;
       setUp(() async {
-        e = new NavNotifyExceptionElement(exception, stacktrace: stacktrace);
+        e = new NavNotifyExceptionElement(exception, stacktrace: stacktrace,
+            queue: queue);
         document.body.append(e);
         await e.onRendered.first;
       });
-      tearDown(() {
+      tearDown(() async {
         sub.cancel();
         e.remove();
+        await e.onRendered.first;
       });
       test('navigation after connect', () async {
         sub = window.onPopState.listen(expectAsync((_) {}, count: 1,