anchor.diff:        Notifications.of(context),
         _pushSnapshotScreenForImport,
       );
  -
  -    // If the animations are null, initialize them.
  -    appBarAnimation ??= defaultAnimationController(
  -      this,
  -      value: isNarrow ? 1.0 : 0.0,
  -    );
  -    appBarCurve ??= defaultCurvedAnimation(appBarAnimation);
  -    if (isNarrow) {
  -      appBarAnimation.forward();
  -    } else {
  -      appBarAnimation.reverse();
  -    }
     }
   
     @override
     void dispose() {
       _tabController?.dispose();
       _currentScreen?.dispose();
  -    appBarAnimation?.dispose();
       _connectVmSubscription?.cancel();
       _showPageSubscription?.cancel();
   
  
positive.code:         onTap: _pushScreenToLocalPageRoute,
          tabs: [for (var screen in widget.tabs) screen.buildTab(context)],
        );
        preferredSize = Tween<Size>(
          begin: const Size.fromHeight(kToolbarHeight),
          end: const Size.fromHeight(kToolbarHeight + 40.0),
        ).evaluate(appBarCurve);
        final animatedAlignment = Tween<Alignment>(
          begin: Alignment.centerRight,
          end: Alignment.bottomLeft,
        ).evaluate(appBarCurve);
  
        final rightAdjust =
            isNarrow ? 0.0 : DevToolsScaffold.actionWidgetSize / 2;
        final animatedRightPadding = Tween<double>(
          begin: math.max(
              0.0,
              DevToolsScaffold.actionWidgetSize * (actions?.length ?? 0.0) -
                  rightAdjust),
          end: 0.0,
        ).evaluate(appBarCurve);
  
        flexibleSpace = Align(
          alignment: animatedAlignment,
          child: Padding(
            padding: EdgeInsets.only(
              top: 4.0,
              right: animatedRightPadding,
            ),
            child: tabBar,
          ),
  
negative.code:     with TickerProviderStateMixin {
    /// A tag used for [Hero] widgets to keep the [AppBar] in the same place
    /// across route transitions.
    static const Object _appBarTag = 'DevTools AppBar';
  
    /// The controller for animating between tabs.
    ///
  