Replace ReceivePorts with asyncStart|End in some tests.

tests/lib/async/intercept_run_async4_test.dart

Index: tests/lib/async/intercept_run_async4_test.dart
diff --git a/tests/lib/async/intercept_run_async4_test.dart b/tests/lib/async/intercept_run_async4_test.dart
index c935bdbc636ebe17aac14c68bc2f025d7a29ebb9..30c4a276089908feef09c201bb3dd229f1bcaa49 100644
--- a/tests/lib/async/intercept_run_async4_test.dart
+++ b/tests/lib/async/intercept_run_async4_test.dart
@@ -2,9 +2,9 @@
 // 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';
 
 var events = [];
 
@@ -26,9 +26,7 @@ handler(fun) {
 }
 
 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();
 
   // Test that body of a runAsync goes to the zone it came from.
   var result = runZonedExperimental(body, onRunAsync: handler);
@@ -43,7 +41,7 @@ main() {
            "handler", "handler done",
            "run nested body"],
           events);
-      port.close();
+      asyncEnd();
     });
   });
 }