anchor.diff:    /// See also:
     ///
     ///  * <https://github.com/dart-lang/sdk/blob/master/runtime/vm/service/service.md#rpcs-requests-and-responses>
  +  @protected
  +  @mustCallSuper
     void initServiceExtensions() {
       assert(!_debugServiceExtensionsRegistered);
       registerSignalServiceExtension(
  
positive.code:   /// no value.
    ///
    /// Calls the `callback` callback when the service extension is called.
    void registerSignalServiceExtension({
      @required String name,
      @required VoidCallback callback
  
negative.code:   ///
    /// Calls the `setter` callback with the new value when the
    /// service extension method is called with a new value.
    @protected
    void registerBoolServiceExtension({
      String name,
      @required ValueGetter<bool> getter,
  