anchor.diff:    void addClass(ClassEntity element, ImportSet importSet) {
       var item = pendingClasses[element];
       if (item == null) {
  -      item = new ClassWorkItem(element, importSet);
  +      item = ClassWorkItem(element, importSet);
         pendingClasses[element] = item;
         queue.add(item);
       } else {
  
positive.code:       String importingUri = source.readString();
        String prefix = source.readString();
        LibraryEntity importingLibrary = source.readLibrary();
        return new ImportDescription.internal(
            importingUri, prefix, importingLibrary);
      });
      source.end(tag);
      return new OutputUnitData(
          isProgramSplit,
          mainOutputUnit,
          classToUnit,
  
negative.code: /// The algorithm work queue.
  class WorkQueue {
    /// The actual queue of work that needs to be done.
    final Queue<WorkItem> queue = Queue();
  
    /// An index to find work items in the queue corresponding to a class.
    final Map<ClassEntity, WorkItem> pendingClasses = {};
  
    /// An index to find work items in the queue corresponding to a member.
    final Map<MemberEntity, WorkItem> pendingMembers = {};
  
    /// An index to find work items in the queue corresponding to a constant.
    final Map<ConstantValue, WorkItem> pendingConstants = {};
  
    /// Lattice used to compute unions of [ImportSet]s.
    final ImportSetLattice _importSets;
  