Added async_helper and fixed broken asynchronous test.

tests/isolate/global_error_handler_stream2_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 test;
 
 import 'package:expect/expect.dart';
 import 'dart:async';
 import 'dart:isolate';
+import '../async_helper.dart';
 
 runTest() {
   IsolateSink mainIsolate;
   stream.listen((msg) {
     mainIsolate = msg;
     throw new UnsupportedError("ignore exception");
   }, onDone: () {
     mainIsolate.add("received done");
     mainIsolate.close();
   });
@@ skipping 10 matching lines @@
   var timer = new Timer(const Duration(seconds: 2), () { throw "failed"; });
 
   var box = new MessageBox();
   IsolateSink otherIsolate = streamSpawnFunction(runTest, globalErrorHandler);
   otherIsolate.add(box.sink);
   // The previous event should have been handled entirely, but the current
   // implementations don't guarantee that and might mix the done event with
   // the handling of the previous event. We therefore delay the closing.
   // Note: if the done is sent too early it won't lead to failing tests, but
   // just won't make sure that the globalErrorHandler works.
-  new Timer(const Duration(milliseconds: 10), otherIsolate.close);
+  asyncStart();
+  new Timer(const Duration(milliseconds: 10), () {
+    otherIsolate.close();
+    asyncEnd();
+  });
+  asyncStart();
   box.stream.single.then((msg) {
     Expect.equals("received done", msg);
     timer.cancel();
     keepRunningBox.stream.close();
+    asyncEnd();
   });
 }