anchor.diff:    static RawReceivePort _receivePort;
     static SendPort _sendPort;
     static int _scheduledWakeupTime;
  +  // Keep track whether at least one message is pending in the event loop. This
  +  // way we do not have to notify for every pending _firstZeroTimer.
  +  static var _messagePending = false;
  +
     static bool _handlingCallbacks = false;
   
     Function _callback;  // Closure to call when timer fires. null if canceled.
  
positive.code:       return;
      }
  
      if (_firstZeroTimer == null && _heap.isEmpty) {
        // No pending timers: Close the receive port and let the event handler
        // know.
        if (_receivePort != null) {
  
negative.code:         _createTimerHandler();
        }
        if (_firstZeroTimer != null) {
          if (!_messagePending) {
            _sendPort.send(null);
            _messagePending = true;  // Reset when the port receives a message.
          }
        } else {
          var wakeupTime = _heap.first._wakeupTime;
          if ((_scheduledWakeupTime == null) ||
  