anchor.diff:    void setupParentData(RenderBox child) {
       if (child.parentData is! BlockParentData)
         child.parentData = new BlockParentData();
  -  }
  -
  -  double computeDistanceToActualBaseline(TextBaseline baseline) {
  -    return defaultComputeDistanceToFirstActualBaseline(baseline);
     }
   
     double _childrenHeight;
  
positive.code:     _childrenHeight = y;
    }
  
    void hitTestChildren(HitTestResult result, { Point position }) {
      defaultHitTestChildren(result, position: position);
    }
  
    void paint(PaintingCanvas canvas, Offset offset) {
      defaultPaint(canvas, offset);
    }
  
  }
  
  class RenderBlock extends RenderBlockBase {
  
negative.code:       return;
      _startOffset = value;
      if (!_inCallback)
        markNeedsPaint();
    }
  
    double getMinIntrinsicWidth(BoxConstraints constraints) {
  