anchor.diff:      if (parent is ClassElement) {
         return parent.lookUpSetter(node.name.name, node.declaredElement.library);
       }
  -    // todo (pq): consider extensions
  +    if (parent is ExtensionElement) {
  +      return parent.getSetter(node.name.name);
  +    }
       return null;
     }
   
  
positive.code:       return parent.lookUpInheritedConcreteSetter(
            node.name.name, node.declaredElement.library);
      }
      // todo (pq): consider extensions
      return null;
    }
  
  
negative.code:     if (parent is ClassElement) {
        return parent.lookUpGetter(node.name.name, node.declaredElement.library);
      }
      if (parent is ExtensionElement) {
        return parent.getSetter(node.name.name);
      }
      return null;
    }
  
  