Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/run_zoned3_test.dart

Index: tests/lib/async/run_zoned3_test.dart
diff --git a/tests/lib/async/run_zoned3_test.dart b/tests/lib/async/run_zoned3_test.dart
index f8802084f56b200477dc040da4d33ddb98754c0d..4545155223c4892f01e2d328803908be4a816d33 100644
--- a/tests/lib/async/run_zoned3_test.dart
+++ b/tests/lib/async/run_zoned3_test.dart
@@ -2,14 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:async_helper/async_helper.dart';
 import "package:expect/expect.dart";
 import 'dart:async';
-import 'dart:isolate';
 
 main() {
-  // We keep a ReceivePort open until all tests are done. This way the VM will
-  // hang if the callbacks are not invoked and the test will time out.
-  var port = new ReceivePort();
+  asyncStart();
   // Ensure that `runZoned` is done when a synchronous call throws.
   bool sawException = false;
   try {
@@ -17,7 +15,7 @@ main() {
                          onDone: () {
                            // onDone is executed synchronously.
                            Expect.isFalse(sawException);
-                           port.close();
+                           asyncEnd();
                          });
   } catch (e) {
     sawException = true;