anchor.diff:      final _ClassData classData = getClassData(cl);
   
       if (allocatedClasses.add(cl)) {
  -      classData.allocatedSubtypes.add(classData);
  +      classData.addAllocatedSubtype(classData);
         classData.invalidateDependentInvocations(_typeFlowAnalysis.workList);
   
         for (var supertype in classData.supertypes) {
  -        supertype.allocatedSubtypes.add(classData);
  +        supertype.addAllocatedSubtype(classData);
           supertype.invalidateDependentInvocations(_typeFlowAnalysis.workList);
         }
   
  
positive.code:   ConcreteType _concreteType;
    ConcreteType get concreteType =>
        _concreteType ??= new ConcreteType(this, class_.rawType);
  
    @override
    int get hashCode => _id;
  
negative.code:   final int _id;
    final Class class_;
    final Set<_ClassData> supertypes; // List of super-types including this.
    final Set<_ClassData> _allocatedSubtypes = new Set<_ClassData>();
  
    /// Flag indicating if this class has a noSuchMethod() method not inherited
    /// from Object.
  