Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/secure_builtin_roots_test.dart

Index: tests/standalone/io/secure_builtin_roots_test.dart
diff --git a/tests/standalone/io/secure_builtin_roots_test.dart b/tests/standalone/io/secure_builtin_roots_test.dart
index be0a467322e519db5112c223d5650eccbddfd935..f7b5cbb4c3ed8b98c6dba28cbaead60ebf5355b7 100644
--- a/tests/standalone/io/secure_builtin_roots_test.dart
+++ b/tests/standalone/io/secure_builtin_roots_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 "package:path/path.dart";
 import "dart:io";
-import "dart:isolate";
 import "dart:async";
 
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
+import "package:path/path.dart";
+
 void main() {
   var args = new Options().arguments;
   if (!args.contains('--child')) {
@@ -80,10 +81,10 @@ void runAllTestsInChildProcesses() {
     });
   }
 
-  ReceivePort keepAlive = new ReceivePort();
+  asyncStart();
   Future.wait([runChild(['--child']),
                runChild(['--child', '--database']),
                runChild(['--child', '--builtin-roots']),
                runChild(['--child', '--builtin-roots', '--database'])])
-      .then((_) => keepAlive.close());
+      .then((_) => asyncEnd());
   }