anchor.diff:  abstract class SceneBuilderRecorder extends Recorder {
     SceneBuilderRecorder({@required String name}) : super._(name, true);
   
  +  @override
  +  Profile get profile => _profile;
  +  Profile _profile;
  +
     /// Called from [Window.onBeginFrame].
     @mustCallSuper
     void onBeginFrame() {}
  
positive.code:   @override
    Future<Profile> run() {
      final Completer<Profile> profileCompleter = Completer<Profile>();
      final Profile profile = Profile(name: name);
  
      window.onBeginFrame = (_) {
        try {
  
negative.code:   void body(Profile profile);
  
    @override
    Profile get profile => _profile;
    Profile _profile;
  
    @override
    @nonVirtual
    Future<Profile> run() async {
      _profile = Profile(name: name);
      do {
        await Future<void>.delayed(Duration.zero);
        body(_profile);
      } while (shouldContinue());
      return _profile;
    }
  }
  
  