Add a test for timers in child isolates.

tools/dom/src/native_DOMImplementation.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.
 
 part of html;
 
 class _Utils {
   static double dateTimeToDouble(DateTime dateTime) =>
       dateTime.millisecondsSinceEpoch.toDouble();
   static DateTime doubleToDateTime(double dateTime) {
@@ skipping 129 matching lines @@
 const _CANCEL_TIMER = 'CANCEL_TIMER';
 const _TIMER_PING = 'TIMER_PING';
 const _PRINT = 'PRINT';
 
 _helperIsolateMain() {
   port.receive((msg, replyTo) {
     final cmd = msg[0];
     if (cmd == _NEW_TIMER) {
       final duration = new Duration(milliseconds: msg[1]);
       bool periodic = msg[2];
-      final callback = () { replyTo.send(_TIMER_PING); };
+      ping() { replyTo.send(_TIMER_PING); };
       _TIMER_REGISTRY[replyTo] = periodic ?
-          new Timer.periodic(duration, callback) :
-          new Timer(duration, callback);
+          new Timer.periodic(duration, (_) { ping(); }) :
+          new Timer(duration, ping);
     } else if (cmd == _CANCEL_TIMER) {
       _TIMER_REGISTRY.remove(replyTo).cancel();
     } else if (cmd == _PRINT) {
       final message = msg[1];
       // TODO(antonm): we need somehow identify those isolates.
       print('[From isolate] $message');
     }
   });
 }
 
 final _printClosure = window.console.log;
 final _pureIsolatePrintClosure = (s) {
   _HELPER_ISOLATE_PORT.then((sendPort) {
     sendPort.send([_PRINT, s]);
   });
 };
 
 final _forwardingPrintClosure = _Utils.forwardingPrint;