anchor.diff:      onMouseDown.listen((e) {
         if (stage != null) {
           _stopScrolling();
  -        _showScrollBars();
           _lastPos.setTo(e.stageX, e.stageY);
           stage.onMouseMove.listen(_stageMouseMoveHandler);
           stage.onMouseUp.listen(_stageMouseUpHandler);
  
positive.code:   Point<num> _viewport;
  
    ScrollView(): super() {
      _hbar = new ScrollBar(orientation: Orientation.HORIZONTAL)..visible = false;
      super.addChildAt(_hbar, 0);
      _vbar = new ScrollBar(orientation: Orientation.VERTICAL)..visible = false;
      super.addChildAt(_vbar, 0);
      _content = new Sprite();
      super.addChildAt(_content, 0);
  
negative.code:   }
  
    void _stopScrolling() {
      _showScrollBars();
      stage.removeEventListener(MouseEvent.MOUSE_MOVE, _stageMouseMoveHandler);
      stage.removeEventListener(MouseEvent.MOUSE_UP, _stageMouseUpHandler);
    }
  