Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/link_async_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 "dart:async";
+import "dart:io";
+
+import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 import "package:path/path.dart";
-import "dart:async";
-import "dart:io";
-import "dart:isolate";
 
 // Test the dart:io Link class.
 
 class FutureExpect {
   static Future isTrue(Future<bool> result) =>
       result.then((value) => Expect.isTrue(value));
   static Future isFalse(Future<bool> result) =>
       result.then((value) => Expect.isFalse(value));
   static Future equals(expected, Future result) =>
       result.then((value) => Expect.equals(expected, value));
@@ skipping 244 matching lines @@
             Expect.equals('Found', v);
           }
         })
       );
     }
   }
   return Future.wait(futures);
 }
 
 main() {
-  ReceivePort keepAlive = new ReceivePort();
+  asyncStart();
   testCreate()
     .then((_) => testCreateLoopingLink())
     .then((_) => testRename())
-    .then((_) => keepAlive.close());
+    .then((_) => asyncEnd());
 }