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