anchor.diff:    }
   
     CustomPaintCallback _callback;
  -  void set callback (CustomPaintCallback value) {
  -    assert(value != null || !attached);
  -    if (_callback == value)
  -      return;
  -    _callback = value;
  +  void set callback (CustomPaintCallback newCallback) {
  +    assert(newCallback != null || !attached);
  +    if (_callback == newCallback)
  +      return;
  +    _callback = newCallback;
       markNeedsPaint();
     }
   
  
positive.code: 
    Color _color;
    Color get color => _color;
    void set color (Color value) {
      assert(value != null);
      if (_color == value)
        return;
      _color = value;
      markNeedsPaint();
    }
  
    sky.TransferMode _transferMode;
    sky.TransferMode get transferMode => _transferMode;
    void set transferMode (sky.TransferMode value) {
      assert(value != null);
      if (_transferMode == value)
        return;
      _transferMode = value;
      markNeedsPaint();
    }
  
  
negative.code:   final BoxPainter _painter;
  
    BoxDecoration get decoration => _painter.decoration;
    void set decoration (BoxDecoration newDecoration) {
      assert(newDecoration != null);
      if (newDecoration == _painter.decoration)
        return;
      _removeBackgroundImageListenerIfNeeded();
      _painter.decoration = newDecoration;
      _addBackgroundImageListenerIfNeeded();
      markNeedsPaint();
    }
  