anchor.diff:      _clear();
       if (!_isInHeap) return;
       assert(_wakeupTime != 0);
  -    bool update = _firstZeroTimer == null && _heap.isFirst(this);
  +    bool update = (_firstZeroTimer == null) && _heap.isFirst(this);
       _heap.remove(this);
       if (update) {
         _notifyEventHandler();
  
positive.code:   bool _addTimerToHeap() {
      if (_wakeupTime == 0) {
        if (_firstZeroTimer == null) {
          _lastZeroTimer = _firstZeroTimer = this;
          return true;
        } else {
          _lastZeroTimer = _lastZeroTimer._indexOrNext = this;
          return false;
        }
      } else {
  
negative.code:     // Collect all pending timers.
      var timer = _firstZeroTimer;
      var nextTimer = _lastZeroTimer;
      _firstZeroTimer = null;
      _lastZeroTimer = null;
      while (_heap.isNotEmpty && _heap.first._wakeupTime <= currentTime) {
        var next = _heap.removeFirst();
        if (timer == null) {
          nextTimer = next;
          timer = next;
        } else {
          nextTimer._indexOrNext = next;
          nextTimer = next;
        }
      }
  
  