anchor.diff:        locale: locale ?? this.locale,
         timeDilation: timeDilation ?? this.timeDilation,
         platform: platform ?? this.platform,
  +      isTestMode: isTestMode ?? this.isTestMode,
       );
     }
   
  
positive.code:     Locale locale,
      double timeDilation,
      TargetPlatform platform,
    }) {
      return GalleryOptions(
        themeMode: themeMode ?? this.themeMode,
  
negative.code:   }
  }
  
  // Everything below is boilerplate except code relating to time dilation and
  // theme changes.
  // See https://medium.com/flutter/managing-flutter-application-state-with-inheritedwidgets-1140452befe1
  
  class _ModelBindingScope extends InheritedWidget {
  