anchor.diff:      markNeedsLayout();
     }
   
  -  BoxConstraints childConstraints(BoxConstraints constraints) {
  +  BoxConstraints _getInnerConstraints(BoxConstraints constraints) {
       return new BoxConstraints(
         minWidth: _minWidth ?? constraints.minWidth,
         maxWidth: _maxWidth ?? constraints.maxWidth,
  
positive.code:     markNeedsLayout();
    }
  
    BoxConstraints _computeChildConstraints(BoxConstraints constraints) {
      return new BoxConstraints(
        minWidth: _widthFactor == null ? constraints.minWidth : constraints.maxWidth * _widthFactor,
        maxWidth: _widthFactor == null ? constraints.maxWidth : constraints.maxWidth * _widthFactor,
  
negative.code: 
    void performLayout() {
      if (child != null)
        child.layout(_getInnerConstraints(constraints));
    }
  
    String debugDescribeSettings(String prefix) {
  