Make isolate tests work on drt (and hopefully dartium).

tests/isolate/spawn_function_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.
 
 // Example of spawning an isolate from a function.
 library spawn_tests;
 import 'dart:isolate';
-import '../../pkg/unittest/lib/unittest.dart';
+import 'package:unittest/unittest.dart';
+import "remote_unittest_helper.dart";
 
 child(args) {
   var msg = args[0];
   var reply = args[1];
   reply.send('re: $msg');
 }
 
-main() {
+void main([args, port]) {
+  if (testRemote(main, port)) return;
   test('message - reply chain', () {
     ReceivePort port = new ReceivePort();
     Isolate.spawn(child, ['hi', port.sendPort]);
     port.listen(expectAsync1((msg) {
       port.close();
       expect(msg, equals('re: hi'));
     }));
   });
 }