Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/catch_errors6_test.dart

Index: tests/lib/async/catch_errors6_test.dart
diff --git a/tests/lib/async/catch_errors6_test.dart b/tests/lib/async/catch_errors6_test.dart
index f9b526184579f7a536f04bc9d8590c466d650916..58c4f742a4a3b3f4c787493fbff03a4dab0eddf3 100644
--- a/tests/lib/async/catch_errors6_test.dart
+++ b/tests/lib/async/catch_errors6_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 completer = new Completer();
   var errorHandlerOrDoneHasBeenExecuted = false;
   // Test that `catchErrors` doesn't shut down if a future is never completed.
@@ -26,6 +24,6 @@ main() {
     });
   Timer.run(() {
     Expect.isFalse(errorHandlerOrDoneHasBeenExecuted);
-    port.close();
+    asyncEnd();
   });
 }