Only notify event-handler when there is an earlier timer in the timer queue.

sdk/lib/io/timer_impl.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.io;
 
 class _Timer extends LinkedListEntry<_Timer> implements Timer {
   // Disables the timer.
   static const int _NO_TIMER = -1;
 
@@ skipping 11 matching lines @@
                             int milliSeconds,
                             bool repeating) {
     _Timer timer = new _Timer._internal();
     timer._callback = callback;
     if (milliSeconds > 0) {
       timer._wakeupTime =
           new DateTime.now().millisecondsSinceEpoch + milliSeconds;
     }
     timer._milliSeconds = repeating ? milliSeconds : -1;
     timer._addTimerToList();
-    timer._notifyEventHandler();
+    if (identical(timer, _timers.first)) {
+      // The new timer is the first in queue. Update event handler.
+      timer._notifyEventHandler();
+    }
     return timer;
   }
 
   factory _Timer(int milliSeconds, void callback(Timer timer)) {
     return _createTimer(callback, milliSeconds, false);
   }
 
   factory _Timer.periodic(int milliSeconds, void callback(Timer timer)) {
     return _createTimer(callback, milliSeconds, true);
   }
@@ skipping 22 matching lines @@
     if (identical(first, this)) {
       _notifyEventHandler();
     }
   }
 
   void _advanceWakeupTime() {
     assert(_milliSeconds >= 0);
     _wakeupTime += _milliSeconds;
   }
 
-  // Adds a timer to the timer list and resets the native timer if it is the
-  // earliest timer in the list. Timers with the same wakeup time are enqueued
-  // in order and notified in FIFO order.
+  // Adds a timer to the timer list. Timers with the same wakeup time are
+  // enqueued in order and notified in FIFO order.
   void _addTimerToList() {
     _Timer entry = _timers.isEmpty ? null : _timers.first;
     while (entry != null) {
       if (_wakeupTime < entry._wakeupTime) {
         entry.insertBefore(this);
         return;
       }
       entry = entry.next;
     }
     _timers.add(this);
@@ skipping 92 matching lines @@
 _getTimerFactoryClosure() {
   return (int milliSeconds, void callback(Timer timer), bool repeating) {
     if (repeating) {
       return new _Timer.periodic(milliSeconds, callback);
     }
     return new _Timer(milliSeconds, callback);
   };
 }