Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/directory_non_ascii_test.dart

Index: tests/standalone/io/directory_non_ascii_test.dart
diff --git a/tests/standalone/io/directory_non_ascii_test.dart b/tests/standalone/io/directory_non_ascii_test.dart
index 9fe3ef08feac92e98c8a8dbee28c845c8c47cad1..e4aede680a80ed011dff28ca067bd812d1d7c1b1 100644
--- a/tests/standalone/io/directory_non_ascii_test.dart
+++ b/tests/standalone/io/directory_non_ascii_test.dart
@@ -2,12 +2,13 @@
 // 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:io';
-import 'dart:isolate';
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
 
 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.
@@ -28,7 +29,7 @@ main() {
               tempDir.delete(recursive: true).then((_) {
                 Expect.isFalse(temp.existsSync());
                 Expect.isFalse(nonAsciiDir.existsSync());
-                port.close();
+                asyncEnd();
               });
             });
           });