Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/process_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();
   var executable = new File(Platform.executable).fullPathSync();
   var tempDir = new Directory('').createTempSync();
   var nonAsciiDir = new Directory('${tempDir.path}/æøå');
   nonAsciiDir.createSync();
   var nonAsciiFile = new File('${nonAsciiDir.path}/æøå.dart');
   nonAsciiFile.writeAsStringSync(
 """
 import 'dart:io';
 
 main() {
   if ('æøå' != new File('æøå.txt').readAsStringSync()) {
     throw new StateError("not equal");
   }
 }
 """);
   var nonAsciiTxtFile = new File('${nonAsciiDir.path}/æøå.txt');
   nonAsciiTxtFile.writeAsStringSync('æøå');
   var script = nonAsciiFile.path;
   Process.run(executable, [script], workingDirectory: nonAsciiDir.path)
       .then((result) {
         Expect.equals(0, result.exitCode);
         tempDir.deleteSync(recursive: true);
-        port.close();
+        asyncEnd();
       });
 }