Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/platform_test.dart

Index: tests/standalone/io/platform_test.dart
diff --git a/tests/standalone/io/platform_test.dart b/tests/standalone/io/platform_test.dart
index 1fdad2ba292a149c1ce50e98c01f573b3e6f274e..6c009e889c0013f0b924338e6296407603169ccd 100644
--- a/tests/standalone/io/platform_test.dart
+++ b/tests/standalone/io/platform_test.dart
@@ -2,11 +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:async";
 import "dart:io";
 import "dart:isolate";
 
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+
 test() {
   Expect.isTrue(Platform.numberOfProcessors > 0);
   var os = Platform.operatingSystem;
@@ -60,7 +62,7 @@ void f() {
 }
 
 testIsolate() {
-  var port = new ReceivePort();
+  asyncStart();
   var sendPort = spawnFunction(f);
   Future.wait([sendPort.call("Platform.executable"),
                sendPort.call("Platform.script"),
@@ -77,7 +79,7 @@ testIsolate() {
     Expect.isTrue(uri.path.endsWith('tests/standalone/io/platform_test.dart'));
     Expect.equals(Platform.packageRoot, results[2]);
     Expect.listEquals(Platform.executableArguments, results[3]);
-    sendPort.call("close").then((_) => port.close());
+    sendPort.call("close").then((_) => asyncEnd());
   });
 }