anchor.diff:    Element get enclosingClassOrCompilationUnit {
       return _unsupported('enclosingClassOrCompilationUnit');
     }
  -
  -  @override
  -  String get fixedBackendName => _unsupported('fixedBackendName');
   
     @override
     LibraryElement get implementationLibrary => library;
  
positive.code: 
    @override
    ElementKind get kind => ElementKind.FACTORY_CONSTRUCTOR;
  }
  
  abstract class MemberElementMixin
  
negative.code: 
    @override
    ElementKind get kind => ElementKind.GENERATIVE_CONSTRUCTOR;
  
    @override
    bool get isEffectiveTargetMalformed =>
        _unsupported('isEffectiveTargetMalformed');
  }
  
  class FactoryConstructorElementZ extends ConstructorElementZ {
  