anchor.diff:      _zone.run(() {
         flags &= ~framePendingFlag;
         flags |= runningFlag;
  -      clock++;
   
         _nextTickCompleter.complete();
         _nextTickCompleter = null;
  
positive.code:       _handleNextTick();
      }
    }
  }
  
negative.code:   static const int framePendingFlag = 1 << 2;
  
    int flags = 0;
    int clock = 1;
  
    bool get isRunning => ((flags & runningFlag) != 0);
  
  