anchor.diff:  
   class ServiceExtensionDescription<T> {
     ServiceExtensionDescription({
  -    @required this.enabledIcon,
  +    required this.enabledIcon,
       disabledIcon,
  -    List<String> displayValues,
  -    @required this.extension,
  -    @required this.title,
  -    @required this.values,
  -    @required this.gaScreenName,
  -    @required this.gaItem,
  -    @required this.tooltip,
  +    List<String>? displayValues,
  +    required this.extension,
  +    required this.title,
  +    required this.values,
  +    required this.gaScreenName,
  +    required this.gaItem,
  +    required this.tooltip,
       this.description,
       this.tooltipUrl,
       this.shouldCallOnAllIsolates = false,
  
positive.code: 
    final List<String> displayValues;
  
    final String gaScreenName; // Analytics screen (screen name where item lives).
  
    final String gaItem; // Analytics item name (toggleable item's name).
  
    String get gaItemTooltipLink => '${gaItem}TooltipLink';
  
  
negative.code: // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // ignore_for_file: import_of_legacy_library_into_null_safe
  
  library service_extensions;
  
  