anchor.diff:    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 = [];
  
positive.code: 
    void addNullLiteral(LintRule linter, AstVisitor visitor) {
      _forNullLiteral.add(new _Subscription(linter, visitor, _getTimer(linter)));
    }
  
    void addParenthesizedExpression(LintRule linter, AstVisitor visitor) {
  
negative.code:         .add(new _Subscription(linter, visitor, _getTimer(linter)));
    }
  
    void addMixinDeclaration(LintRule linter, AstVisitor visitor) {
      _forMixinDeclaration
          .add(new _Subscription(linter, visitor, _getTimer(linter)));
    }
  
    void addNamedExpression(LintRule linter, AstVisitor visitor) {
      _forNamedExpression
          .add(new _Subscription(linter, visitor, _getTimer(linter)));
  