anchor.diff:      return new SectorDimensions.withConstraints(constraints);
     }
   
  -  SectorConstraints get constraints { SectorConstraints result = super.constraints; return result; }
  +  SectorConstraints get constraints => super.constraints;
     void performResize() {
       // default behaviour for subclasses that have sizedByParent = true
       deltaRadius = constraints.constrainDeltaRadius(0.0);
  
positive.code:   double constrainDeltaTheta(double deltaTheta) {
      return clamp(min: minDeltaTheta, max: maxDeltaTheta, value: deltaTheta);
    }
  }
  
  class SectorDimensions {
  
negative.code: 
  const double kTwoPi = 2 * math.PI;
  
  class SectorConstraints extends Constraints {
    const SectorConstraints({
      this.minDeltaRadius: 0.0,
      this.maxDeltaRadius: double.INFINITY,
  