anchor.diff:  /**
    * An [AbstractClassElementImpl] which is a class.
    */
  -class ClassElementImpl extends AbstractClassElementImpl {
  +class ClassElementImpl extends AbstractClassElementImpl
  +    with TypeParameterizedElementMixin {
     /**
      * The unlinked representation of the class in the summary.
      */
  
positive.code:   }
  
    @override
    List<TypeParameterElement> get typeParameters {
      if (_unlinkedClass != null) {
        return resynthesizedTypeParameters;
      }
      return _typeParameters;
    }
  
negative.code:    * A list containing all of the fields contained in this class.
     */
    List<FieldElement> _fields = FieldElement.EMPTY_LIST;
  
    /**
     * The type defined by the class.
  