Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/directory_list_pause_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:expect/expect.dart";
 import "dart:async";
 import "dart:io";
-import "dart:isolate";
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
 
 
 void testPauseList() {
-  var keepAlive = new ReceivePort();
+  asyncStart();
   // TOTAL should be bigger the our directory listing buffer.
   const int TOTAL = 128;
   new Directory("").createTemp().then((d) {
     for (int i = 0; i < TOTAL; i++) {
       new Directory("${d.path}/$i").createSync();
       new File("${d.path}/$i/file").createSync();
     }
     bool first = true;
     var subscription;
     int count = 0;
     subscription = d.list(recursive: true).listen((file) {
       if (file is File) {
         if (first) {
           first = false;
           subscription.pause();
           Timer.run(() {
             for (int i = 0; i < TOTAL; i++) {
               new File("${d.path}/$i/file").deleteSync();
             }
             subscription.resume();
           });
         }
         count++;
       }
     }, onDone: () {
       Expect.notEquals(TOTAL, count);
       Expect.isTrue(count > 0);
-      d.delete(recursive: true).then((ignore) => keepAlive.close());
+      d.delete(recursive: true).then((ignore) => asyncEnd());
     });
   });
 }
 
 void main() {
   testPauseList();
 }