anchor.diff:      markNeedsLayout();
     }
   
  -  BoxConstraints childConstraints(BoxConstraints constraints) {
  +  BoxConstraints _getInnerConstraints(BoxConstraints constraints) {
       return new BoxConstraints(
         minWidth: _minWidth ?? constraints.minWidth,
         maxWidth: _maxWidth ?? constraints.maxWidth,
  
positive.code: 
    void performLayout() {
      if (child != null)
        child.layout(childConstraints(constraints));
    }
  
    String debugDescribeSettings(String prefix) {
  
negative.code: 
    double getMinIntrinsicWidth(BoxConstraints constraints) {
      if (child != null)
        return child.getMinIntrinsicWidth(_getInnerConstraints(constraints));
      return _getInnerConstraints(constraints).constrainWidth(0.0);
    }
  
    double getMaxIntrinsicWidth(BoxConstraints constraints) {
      if (child != null)
        return child.getMaxIntrinsicWidth(_getInnerConstraints(constraints));
      return _getInnerConstraints(constraints).constrainWidth(0.0);
    }
  
    double getMinIntrinsicHeight(BoxConstraints constraints) {
      if (child != null)
        return child.getMinIntrinsicHeight(_getInnerConstraints(constraints));
      return _getInnerConstraints(constraints).constrainHeight(0.0);
    }
  
    double getMaxIntrinsicHeight(BoxConstraints constraints) {
      if (child != null)
        return child.getMaxIntrinsicHeight(_getInnerConstraints(constraints));
      return _getInnerConstraints(constraints).constrainHeight(0.0);
    }
  
    void performLayout() {
      if (child != null) {
        child.layout(_getInnerConstraints(constraints), parentUsesSize: true);
        size = child.size;
      } else {
        size = _getInnerConstraints(constraints).constrain(Size.zero);
      }
    }
  
  