Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/catch_errors16_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 = new StreamController();
   Stream stream = controller.stream;
   // Test that the subscription of a stream is what counts. The error (2) runs
   // through the map-stream which goes through the nested `catchError` but
   // the nested `catchError` won't see the error.
   catchErrors(() {
     stream = stream.map((x) => x + 100);
   }).listen((x) { events.add(x); });
   stream
     .transform(new StreamTransformer(
         handleError: (e, sink) => sink.add("error $e")))
     .listen((x) { events.add("stream $x"); },
             onDone: () {
               Expect.listEquals(["stream 101",
                                 "stream error 2",
                                 ],
                                 events);
-              port.close();
+              asyncEnd();
             });
   controller.add(1);
   controller.addError(2);
   controller.close();
 }