anchor.diff:    final NullabilitySuffix _nullabilitySuffix;
     final LibraryElement _coreLibrary;
     final LibraryElement _asyncLibrary;
  +
  +  ClassElement _futureElement;
  +  ClassElement _futureOrElement;
  +  ClassElement _iterableElement;
  +  ClassElement _mapElement;
  +  ClassElement _streamElement;
   
     InterfaceType _boolType;
     InterfaceType _deprecatedType;
  
positive.code:     return _listType;
    }
  
    @override
    InterfaceType get mapObjectObjectType {
      return _mapObjectObjectType ??=
          mapType.instantiate(<DartType>[objectType, objectType]);
    }
  
    @override
  
negative.code: 
    @override
    InterfaceType get streamDynamicType {
      _streamDynamicType ??= InterfaceTypeImpl.explicit(
        streamElement,
        [dynamicType],
        nullabilitySuffix: _nullabilitySuffix,
      );
      return _streamDynamicType;
    }
  
    ClassElement get streamElement {
      return _streamElement ??= _getClassElement(_asyncLibrary, 'Stream');
    }
  
    @override
  