Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/catch_errors24_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 = [];
   StreamController controller;
   Stream stream;
   // Test that the first listen on a `asBroadcastStream` determines the
   // zone the subscription lives in. In this case the outer listen happens first
   // and the error reaches `handleError`.
   catchErrors(() {
     catchErrors(() {
       controller = new StreamController();
       stream = controller.stream
@@ skipping 19 matching lines @@
   }).listen((x) { events.add("outer: $x"); },
             onDone: () {
               Expect.listEquals(["map 1",
                                  "stream2 101",
                                  "stream 101",
                                  "stream2 error 2",
                                  "stream error 2",
                                  "inner done",
                                 ],
                                 events);
-              port.close();
+              asyncEnd();
             });
 }