Add Zone support for Timers.

sdk/lib/async/event_loop.dart

 // Copyright (c) 2013, 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 dart.async;
 
 typedef void _AsyncCallback();
 
 bool _callbacksAreEnqueued = false;
 Queue<_AsyncCallback> _asyncCallbacks = new Queue<_AsyncCallback>();
 
 void _asyncRunCallback() {
   // As long as we are iterating over the registered callbacks we don't
   // unset the [_callbacksAreEnqueued] boolean.
   while (!_asyncCallbacks.isEmpty) {
     Function callback = _asyncCallbacks.removeFirst();
     try {
       callback();
     } catch (e) {
       _AsyncRun._enqueueImmediate(_asyncRunCallback);
-      throw;
+      rethrow;
     }
   }
   // Any new callback must register a callback function now.
   _callbacksAreEnqueued = false;
 }
 
 void _scheduleAsyncCallback(callback) {
   // Optimizing a group of Timer.run callbacks to be executed in the
   // same Timer callback.
   _asyncCallbacks.add(callback);
@@ skipping 23 matching lines @@
  *     }
  */
 void runAsync(void callback()) {
   _Zone._current.runAsync(callback);
 }
 
 class _AsyncRun {
   /** Enqueues the given callback before any other event in the event-loop. */
   external static void _enqueueImmediate(void callback());
 }