Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/catch_errors21_test.dart

Index: tests/lib/async/catch_errors21_test.dart
diff --git a/tests/lib/async/catch_errors21_test.dart b/tests/lib/async/catch_errors21_test.dart
index 28dec7f71ed98e21a770b5966c5a8ced221b6f24..932a80b2822c1ec51b82ded2b5221faa1dd0db9e 100644
--- a/tests/lib/async/catch_errors21_test.dart
+++ b/tests/lib/async/catch_errors21_test.dart
@@ -2,15 +2,13 @@
 // 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';
 import 'catch_errors.dart';
 
 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();
   var events = [];
   var controller = new StreamController();
   // Test that stream errors, as a result of bad user-code (`map`) are correctly
@@ -34,7 +32,7 @@ main() {
                                  "done",
                                 ],
                                 events);
-              port.close();
+              asyncEnd();
             });
   [1, 2, 3, 4].forEach(controller.add);
   controller.close();