Add Timer implementation for dart2js. Also moves tests to appropriate location.

lib/isolate/isolate_dart2js.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.
 
 
 /**
  * The `dart:isolate` library defines APIs to spawn and communicate with
  * isolates.
  *
  * All code in dart runs in the context of an isolate. Each isolate has its own
@@ skipping 25 matching lines @@
  */
 #library("dart:isolate");
 
 #import("dart:uri");
 #source("isolate_api.dart");
 #source("timer.dart");
 #source("timer_hook.dart");
 #source("serialization.dart");
 #source("dart2js/compiler_hooks.dart");
 #source("dart2js/isolateimpl.dart");
+#source("dart2js/messages.dart");
 #source("dart2js/ports.dart");
-#source("dart2js/messages.dart");
+#source("dart2js/timer_provider.dart");
 
 /**
  * Called by the compiler to support switching
  * between isolates when we get a callback from the DOM.
  */
 void _callInIsolate(_IsolateContext isolate, Function function) {
   isolate.eval(function);
   _globalState.topEventLoop.run();
 }
 
 /**
  * Called by the compiler to fetch the current isolate context.
  */
 void _currentIsolate() => _globalState.currentContext;