Use Timer and not AnimationFrame during Observatory UI tests

runtime/observatory/tests/observatory_ui/vm_connect_target/element_test.dart

Index: runtime/observatory/tests/observatory_ui/vm_connect_target/element_test.dart
diff --git a/runtime/observatory/tests/observatory_ui/vm_connect_target/element_test.dart b/runtime/observatory/tests/observatory_ui/vm_connect_target/element_test.dart
index d5c9080b9c54e034cccac3479e4d46979fee741d..7410a233ab49c419c5ca59a261c2655da8eeea7e 100644
--- a/runtime/observatory/tests/observatory_ui/vm_connect_target/element_test.dart
+++ b/runtime/observatory/tests/observatory_ui/vm_connect_target/element_test.dart
@@ -5,11 +5,15 @@ import 'dart:html';
 import 'dart:async';
 import 'package:unittest/unittest.dart';
 import 'package:observatory/service_html.dart';
+import 'package:observatory/src/elements/helpers/rendering_queue.dart';
 import 'package:observatory/src/elements/vm_connect_target.dart';
 
 main() {
   VMConnectTargetElement.tag.ensureRegistration();
 
+  final TimedRenderingBarrier barrier = new TimedRenderingBarrier();
+  final RenderingQueue queue = new RenderingQueue.fromBarrier(barrier);
+
   WebSocketVMTarget t;
   setUp(() {
     t = new WebSocketVMTarget("a network address");
@@ -37,7 +41,8 @@ main() {
     });
   });
   test('elements created after attachment', () async {
-    final VMConnectTargetElement e = new VMConnectTargetElement(t);
+    final VMConnectTargetElement e = new VMConnectTargetElement(t,
+        queue: queue);
     document.body.append(e);
     await e.onRendered.first;
     expect(e.children.length, isNonZero, reason: 'has elements');
@@ -49,13 +54,14 @@ main() {
     VMConnectTargetElement e;
     StreamSubscription sub;
     setUp(() async {
-      e = new VMConnectTargetElement(t);
+      e = new VMConnectTargetElement(t, 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,