anchor.diff:      this.backgroundDecoration,
       this.gaplessPlayback = false,
       this.customSize,
  +    this.reverse = false,
       this.pageController,
       this.onPageChanged,
       this.scaleStateChangedCallback,
  
positive.code:   @override
    Widget build(BuildContext context) {
      return PageView.builder(
        controller: _controller,
        onPageChanged: widget.onPageChanged,
        itemCount: itemCount,
  
negative.code:   /// Mirror to [PhotoView.gaplessPlayback]
    final bool gaplessPlayback;
  
    /// Mirror to [PageView.reverse]
    final bool reverse;
  
    /// An object that controls the [PageView] inside [PhotoViewGallery]
    final PageController pageController;
  
  