anchor.diff:    // See https://github.com/dart-lang/sdk/issues/41823.
     /// Whether http timeline logging is enabled.
     ValueListenable<bool> get httpTimelineLoggingEnabled =>
  -      _httpTimelineLoggingEnabledNotifier;
  -  final _httpTimelineLoggingEnabledNotifier = ValueNotifier<bool>(false);
  -
  -  // TODO(kenz): change these streams to ValueListenables or remove altogether
  -  // if we can refactor the FlutterFramesChart to be written with more idiomatic
  -  // Flutter.
  -
  -  /// Stream controller that notifies the timeline has been processed.
  -  Stream<bool> get onTimelineProcessed => _timelineProcessedController.stream;
  -  final _timelineProcessedController = StreamController<bool>.broadcast();
  -
  -  /// Stream controller that notifies that offline data was loaded into the
  -  /// timeline.
  -  ///
  -  /// Subscribers to this stream will be responsible for updating the UI for the
  -  /// new value of [timelineData].
  -  Stream<OfflineTimelineData> get onLoadOfflineData =>
  -      _loadOfflineDataController.stream;
  -  final _loadOfflineDataController =
  -      StreamController<OfflineTimelineData>.broadcast();
  -
  -  /// Stream controller that notifies the timeline screen when a non-fatal error
  -  /// should be logged for the timeline.
  -  final _nonFatalErrorController = StreamController<String>.broadcast();
  -
  -  Stream<String> get onNonFatalError => _nonFatalErrorController.stream;
  -
  -  /// Stream controller that notifies the timeline has been cleared.
  -  final _clearController = StreamController<bool>.broadcast();
  -
  -  Stream<bool> get onTimelineCleared => _clearController.stream;
  +      _httpTimelineLoggingEnabled;
  +  final _httpTimelineLoggingEnabled = ValueNotifier<bool>(false);
   
     // TODO(kenz): switch to use VmFlagManager-like pattern once
     // https://github.com/dart-lang/sdk/issues/41822 is fixed.
  
positive.code: 
      // Set offline data.
      setOfflineData();
  
      _loadOfflineDataController.add(offlineTimelineData);
    }
  
    int _threadIdForEvents(
  
negative.code:   final _emptyTimeline = ValueNotifier<bool>(false);
  
    /// Whether the timeline is currently being recorded.
    ValueListenable<bool> get refreshing => _refreshing;
    final _refreshing = ValueNotifier<bool>(false);
  
    /// Whether the recorded timeline data is currently being processed.
    ValueListenable<bool> get processing => _processing;
    final _processing = ValueNotifier<bool>(false);
  
    // TODO(jacobr): this isn't accurate. Another page of DevTools
    // or a different instance of DevTools could change this value. We need to
  