anchor.diff:  class ToggleableServiceExtensionDescription<T>
       extends ServiceExtensionDescription {
     ToggleableServiceExtensionDescription._({
  -    @required Widget enabledIcon,
  -    Widget disabledIcon,
  -    @required String extension,
  -    @required String title,
  -    @required T enabledValue,
  -    @required T disabledValue,
  -    @required String gaScreenName,
  -    @required String gaItem,
  -    @required String tooltip,
  -    String description,
  -    String tooltipUrl,
  +    required Widget enabledIcon,
  +    Widget? disabledIcon,
  +    required String extension,
  +    required String title,
  +    required T enabledValue,
  +    required T disabledValue,
  +    required String? gaScreenName,
  +    required String? gaItem,
  +    required String tooltip,
  +    String? description,
  +    String? tooltipUrl,
       bool shouldCallOnAllIsolates = false,
       this.inverted = false,
     }) : super(
  
positive.code: 
    final String tooltip;
  
    final String description;
  
    final String tooltipUrl;
  }
  
  final debugAllowBanner = ToggleableServiceExtensionDescription<bool>._(
  
negative.code:   slowAnimations,
  ].map((extension) => extension.extension).toSet();
  
  bool isUnsafeBeforeFirstFlutterFrame(String? extensionName) {
    return _unsafeBeforeFirstFrameFlutterExtensions.contains(extensionName);
  }
  
  