anchor.diff:  
     @override
     List<LibraryElement> get visibleLibraries {
  -    Set<LibraryElement> visibleLibraries = new Set();
  +    HashSet<LibraryElement> visibleLibraries = new HashSet<LibraryElement>();
       _addVisibleLibraries(visibleLibraries, false);
  -    return new List.from(visibleLibraries);
  +    return visibleLibraries.toList(growable: false);
     }
   
     @override
  
positive.code:       ResynthesizerContext context = enclosingUnit.resynthesizerContext;
        _mixins = _unlinkedClass.mixins
            .map((EntityRef t) => context.resolveTypeRef(t, this))
            .toList();
      }
      return _mixins ?? const <InterfaceType>[];
    }
  
negative.code:    * element's type parameters.
     */
    List<TypeParameterType> get typeParameterTypes {
      return _typeParameterTypes ??= typeParameters
          .map((TypeParameterElement e) => e.type)
          .toList(growable: false);
    }
  
    /**
  