anchor.diff:    /// - Perform some sanity checking.
     /// Do this after the topological sort so that super types always occur
     /// before subtypes.
  -  void _initialize2(
  +  void _initializeTopologicallySortedClasses(
         Iterable<Class> classes, int expectedStartingTopologicalIndex) {
       int i = expectedStartingTopologicalIndex;
       for (Class class_ in classes) {
  
positive.code:       }
      }
  
      // Add the new classes
      List<Class> addedClassesSorted = new List<Class>();
      int expectedStartIndex = _topSortIndex;
      for (Class class_ in addedClasses) {
        _topologicalSortVisit(class_, new Set<Class>(),
            orderedList: addedClassesSorted);
      }
      _initialize2(addedClassesSorted, expectedStartIndex);
  
      return this;
    }
  
negative.code:       }
      }
  
      _initializeTopologicallySortedClasses(_infoFor.keys, 0);
    }
  
    /// - Build index of direct children.
  