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:   double getMaxIntrinsicHeight(BoxConstraints constraints) {
      return constraints.constrainHeight();
    }
  
    bool get sizedByParent => true;
  
  
negative.code:   void paint(PaintingCanvas canvas, Offset offset) {
      canvas.save();
      canvas.clipRect(offset & size);
      defaultPaint(canvas, offset.translate(0.0, startOffset));
      canvas.restore();
    }
  
    void hitTestChildren(HitTestResult result, { Point position }) {
      defaultHitTestChildren(result, position: position + new Offset(0.0, -startOffset));
    }
  
  }
  
  