Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/catch_errors_test.dart

Index: tests/lib/async/catch_errors_test.dart
diff --git a/tests/lib/async/catch_errors_test.dart b/tests/lib/async/catch_errors_test.dart
index c981966663a3b66d8cd7ede2690daf4d192aee56..f4e0eef4ad4edd8ea78700c3cd684d0188495bc1 100644
--- a/tests/lib/async/catch_errors_test.dart
+++ b/tests/lib/async/catch_errors_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();
   // Make sure `catchErrors` shuts down the error stream when the synchronous
   // operation is done and there isn't any asynchronous pending callback.
   catchErrors(() {
@@ -19,6 +17,6 @@ main() {
       Expect.fail("Unexpected callback");
     },
     onDone: () {
-      port.close();
+      asyncEnd();
     });
 }