Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/secure_builtin_roots_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 "dart:async";
+
+import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 import "package:path/path.dart";
-import "dart:io";
-import "dart:isolate";
-import "dart:async";
 
 void main() {
   var args = new Options().arguments;
   if (!args.contains('--child')) {
     runAllTestsInChildProcesses();
   } else {
     InitializeSSL(useDatabase: args.contains('--database'),
                   useBuiltinRoots: args.contains('--builtin-roots'));
     testGoogleUrl(args.contains('--builtin-roots'));
   }
@@ skipping 53 matching lines @@
         print("Client failed");
         print("  stdout:");
         print(result.stdout);
         print("  stderr:");
         print(result.stderr);
         Expect.fail('Client subprocess exit code: ${result.exitCode}');
       }
     });
   }
 
-  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());
   }