anchor.diff:  
       if (res == AL.Result.success) {
         markNeedsLayout();
  +      _explicitConstraints.add(constraint);
  +    }
  +
  +    return res;
  +  }
  +
  +  /// Removes all explicitly added constraints.
  +  AL.Result clearAllConstraints() {
  +    AL.Result res = _solver.removeConstraints(_explicitConstraints);
  +
  +    if (res == AL.Result.success) {
  +      markNeedsLayout();
  +      _explicitConstraints = new List<AL.Constraint>();
       }
   
       return res;
  
positive.code: 
      if (res == AL.Result.success) {
        markNeedsLayout();
      }
  
      return res;
  
negative.code:          _AutoLayoutParamMixin {
  
    final AL.Solver _solver = new AL.Solver();
    List<AL.Constraint> _explicitConstraints = new List<AL.Constraint>();
  
    RenderAutoLayout({List<RenderBox> children}) {
      _setupLayoutParameters(this);
  