anchor.diff:    StaticTypeContext? _cachedTypeContext;
     final Library _coreLibrary;
     final InterfaceType _nonNullableTypeType;
  +  final List<_AsyncStarFrame> _asyncStarFrames = [];
  +  bool _enclosingIsAsyncStar = false;
  +  late final controllerNullableObjectType = InterfaceType(
  +      coreTypes.index.getClass('dart:async', 'StreamController'),
  +      Nullability.nonNullable,
  +      [coreTypes.objectNullableRawType]);
  +  late final completerBoolType = InterfaceType(
  +      coreTypes.index.getClass('dart:async', 'Completer'),
  +      Nullability.nonNullable,
  +      [coreTypes.boolNonNullableRawType]);
   
     StaticTypeContext get typeContext =>
         _cachedTypeContext ??= StaticTypeContext(_currentMember!, env);
  
positive.code:   TreeNode visitForInStatement(ForInStatement stmt) {
      return _lowerForIn(stmt);
    }
  }
  
negative.code: import 'package:kernel/class_hierarchy.dart';
  import 'package:kernel/core_types.dart';
  import 'package:kernel/type_environment.dart';
  import 'package:kernel/type_algebra.dart';
  
  void transformLibraries(
      List<Library> libraries, CoreTypes coreTypes, ClassHierarchy hierarchy) {
  