Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/catch_errors21_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // 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
   // caught by `catchErrors`. Note that the values are added outside both
   // `catchErrors`, but since the `listen` happens in the most nested
   // `catchErrors` it is caught there.
   catchErrors(() {
     catchErrors(() {
       controller.stream.map((x) { throw x; }).listen((x) {
         // Should not happen.
         events.add("bad: $x");
       });
     }).listen((x) { events.add("caught: $x"); },
               onDone: () { events.add("done"); });
   }).listen((x) { events.add("outer: $x"); },
             onDone: () {
               Expect.listEquals(["caught: 1",
                                  "caught: 2",
                                  "caught: 3",
                                  "caught: 4",
                                  "done",
                                 ],
                                 events);
-              port.close();
+              asyncEnd();
             });
   [1, 2, 3, 4].forEach(controller.add);
   controller.close();
 }