Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/directory_non_ascii_test.dart

 // Copyright (c) 2012, 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:io';
+
+import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
-import 'dart:io';
-import 'dart:isolate';
 
 main() {
-  var port = new ReceivePort();
+  asyncStart();
 
   // On MacOS you get the decomposed utf8 form of file and directory
   // names from the system. Therefore, we have to check for both here.
   var precomposed = 'æøå';
   var decomposed = new String.fromCharCodes([47, 230, 248, 97, 778]);
 
   new Directory('').createTemp().then((tempDir) {
     var nonAsciiDir = new Directory("${tempDir.path}/æøå");
     nonAsciiDir.exists().then((e) {
       Expect.isFalse(e);
       nonAsciiDir.create().then((_) {
         nonAsciiDir.exists().then((e) {
           Expect.isTrue(e);
           new Directory("${tempDir.path}/æøå").createTemp().then((temp) {
             Expect.isTrue(temp.path.contains(precomposed) ||
                           temp.path.contains(decomposed));
             temp.delete().then((_) {
               tempDir.delete(recursive: true).then((_) {
                 Expect.isFalse(temp.existsSync());
                 Expect.isFalse(nonAsciiDir.existsSync());
-                port.close();
+                asyncEnd();
               });
             });
           });
         });
       });
     });
   });
 }