Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/run_async4_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.
 
 library run_async_test;
 
+import 'package:async_helper/async_helper.dart';
 import 'dart:async';
 import 'dart:isolate';
 
 void startTest(SendPort finishPort, replyPort) {
   int invokedCallbacks = 0;
 
   for (int i = 0; i < 100; i++) {
     runAsync(() {
       invokedCallbacks++;
       if (invokedCallbacks == 100) finishPort.send("done");
       if (i == 50) throw new UnsupportedError("ignore exception");
     });
   }
 }
 
 runTest() {
   port.receive(startTest);
 }
 
 bool globalErrorHandler(IsolateUnhandledException e) {
   return e.source is UnsupportedError && e.source.message == "ignore exception";
 }
 
 main() {
+  asyncStart();
   var port = new ReceivePort();
   var timer;
   SendPort otherIsolate = spawnFunction(runTest, globalErrorHandler);
   otherIsolate.send(port.toSendPort());
-  port.receive((msg, replyPort) { port.close(); timer.cancel(); });
+  port.receive((msg, replyPort) {
+    port.close();
+    timer.cancel();
+    asyncEnd();
+  });
   timer = new Timer(const Duration(seconds: 2), () { throw "failed"; });
 }