Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/file_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() {
-  ReceivePort 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) {
       Directory nonAsciiDir = new Directory('${tempDir.path}/æøå');
       nonAsciiDir.create().then((nonAsciiDir) {
         nonAsciiDir.exists().then((result) {
           Expect.isTrue(result);
           File nonAsciiFile = new File('${nonAsciiDir.path}/æøå.txt');
           nonAsciiFile.writeAsString('æøå').then((_) {
             nonAsciiFile.exists().then((result) {
               Expect.isTrue(result);
               nonAsciiFile.readAsString().then((contents) {
                 // The contents of the file is precomposed utf8.
                 Expect.equals(precomposed, contents);
                 nonAsciiFile.create().then((_) {
                   var d = nonAsciiFile.directory;
                   Expect.isTrue(d.path.endsWith(precomposed) ||
                                 d.path.endsWith(decomposed));
                   nonAsciiFile.length().then((length) {
                     Expect.equals(6, length);
                     nonAsciiFile.lastModified().then((_) {
                       nonAsciiFile.fullPath().then((path) {
                         Expect.isTrue(path.endsWith('${precomposed}.txt') ||
                                       path.endsWith('${decomposed}.txt'));
                         tempDir.delete(recursive: true).then((_) {
-                        port.close();
+                        asyncEnd();
                       });
                     });
                   });
                 });
               });
             });
           });
         });
       });
     });
   }).catchError((e) {
     port.close();
     Expect.fail("File not found");
   });
 }