Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/file_stat_test.dart

Index: tests/standalone/io/file_stat_test.dart
diff --git a/tests/standalone/io/file_stat_test.dart b/tests/standalone/io/file_stat_test.dart
index 7b3e33194f718efbb91ac754d0f548d8374c4f1a..afd1b67a0adaf9b0f4c7e5e45985847338ab44eb 100644
--- a/tests/standalone/io/file_stat_test.dart
+++ b/tests/standalone/io/file_stat_test.dart
@@ -4,11 +4,12 @@
 //
 // Dart test program for testing dart:io FileSystemEntity.Stat().
 
-import "package:expect/expect.dart";
-import "package:path/path.dart";
 import 'dart:async';
 import 'dart:io';
-import 'dart:isolate';
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+import "package:path/path.dart";
 
 void testStat() {
   Directory directory = new Directory("").createTempSync();
@@ -119,7 +120,7 @@ Future testStatAsync() {
 
 
 void main() {
-  ReceivePort keepAlive = new ReceivePort();
+  asyncStart();
   testStat();
-  testStatAsync().then((_) => keepAlive.close());
+  testStatAsync().then((_) => asyncEnd());
 }