Fixed NullPointerException in Timer.

runtime/bin/timer_impl.dart

 // Copyright (c) 2011, 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.
 
 class _Timer implements Timer {
 
   /*
    * Set jitter to wake up timer events that would happen in _TIMER_JITTER ms.
    */
   static final int _TIMER_JITTER = 0;
@@ skipping 75 matching lines @@
         }
         entry = entry.nextEntry();
       }
       _timers.addLast(this);
     }
   }
 
 
   void _notifyEventHandler() {
     if (_timers.firstEntry() === null) {
-      EventHandler._sendData(-1, _receivePort, _NO_TIMER);
-      _shutdownTimerHandler();
+      if (_receivePort != null) {
+        EventHandler._sendData(-1, _receivePort, _NO_TIMER);
+        _shutdownTimerHandler();
+      }
     } else {
       EventHandler._sendData(-1,
                              _receivePort,
                              _timers.firstEntry().element._wakeupTime);
     }
   }
 
 
   /*
    * Creates a receive port and registers the timer handler on that receive
    * port.
    */
   void _createTimerHandler() {
 
     void _handleTimeout() {
       int currentTime = (new Date.now()).value + _TIMER_JITTER;
 
       DoubleLinkedQueueEntry<_Timer> entry = _timers.firstEntry();
-      DoubleLinkedQueueEntry<_Timer> current;
       while (entry !== null) {
-        current = entry;
-        _Timer timer = current.element;
-        entry = entry.nextEntry();
+        _Timer timer = entry.element;
         if (timer._wakeupTime <= currentTime) {
-          current.remove();
-          (current.element._callback)(current.element);
-          if (current.element._repeating) {
-            current.element._advanceWakeupTime();
+          entry.remove();
+          timer._callback(timer);
+          // Always process the event with the earliest wakeupTime first.
+          entry = _timers.firstEntry();
+          if (timer._repeating) {
+            timer._advanceWakeupTime();
             timer._addTimerToList();
             _notifyEventHandler();
           }
         } else {
           break;
         }
       }
       _notifyEventHandler();
     }
 
@@ skipping 17 matching lines @@
   static DoubleLinkedQueue<_Timer> _timers;
 
   static ReceivePort _receivePort;
 
   var _callback;
   int _milliSeconds;
   int _wakeupTime;
   bool _repeating;
 }