anchor.diff:    }
   
     @override
  +  void visitMixinDeclaration(MixinDeclaration node) {
  +    _runSubscriptions(node, registry._forMixinDeclaration);
  +    super.visitMixinDeclaration(node);
  +  }
  +
  +  @override
     void visitNamedExpression(NamedExpression node) {
       _runSubscriptions(node, registry._forNamedExpression);
       super.visitNamedExpression(node);
  
positive.code:         .add(new _Subscription(linter, visitor, _getTimer(linter)));
    }
  
    void addNamedExpression(LintRule linter, AstVisitor visitor) {
      _forNamedExpression
          .add(new _Subscription(linter, visitor, _getTimer(linter)));
  
negative.code:   final List<_Subscription<MapLiteralEntry>> _forMapLiteralEntry = [];
    final List<_Subscription<MethodDeclaration>> _forMethodDeclaration = [];
    final List<_Subscription<MethodInvocation>> _forMethodInvocation = [];
    final List<_Subscription<MixinDeclaration>> _forMixinDeclaration = [];
    final List<_Subscription<NamedExpression>> _forNamedExpression = [];
    final List<_Subscription<NullLiteral>> _forNullLiteral = [];
    final List<_Subscription<OnClause>> _forOnClause = [];
    final List<_Subscription<ParenthesizedExpression>>
        _forParenthesizedExpression = [];
    final List<_Subscription<PartDirective>> _forPartDirective = [];
  