anchor.diff:    final ChangeDetectorRef _changeDetector;
     final ViewContainerRef _viewContainer;
     final Disposer _disposer = Disposer.oneShot();
  +  final Disposer _visibleDisposer = Disposer.multi();
     final NgZone _ngZone;
     final OverlayService _overlayService;
     final DomService _domService;
  
positive.code:     if (_repositionLoopId != null) {
        window.cancelAnimationFrame(_repositionLoopId);
      }
      _layoutInternalSub?.cancel();
      _layoutChangeSub?.cancel();
      _windowResizeSub?.cancel();
      _disposer.dispose();
      _animationTimer?.cancel();
      _isVisible = false;
  
negative.code: 
    final List<RelativePosition> _defaultPreferredPositions;
    RelativePosition _alignmentPosition;
  
    OverlayRef _overlayRef;
  
  