anchor.diff:      }
       scanner.expectChar($rparen);
   
  +    _inParentheses = wasInParentheses;
       return new ArgumentInvocation(positional, named, scanner.spanFrom(start),
           rest: rest, keywordRest: keywordRest);
     }
  
positive.code: 
    /// Consumes an argument invocation.
    ArgumentInvocation _argumentInvocation() {
      var start = scanner.state;
      scanner.expectChar($lparen);
      whitespace();
  
negative.code: 
    /// Consumes a parenthesized expression.
    Expression _parentheses() {
      var wasInParentheses = _inParentheses;
      _inParentheses = true;
      try {
        var start = scanner.state;
        scanner.expectChar($lparen);
        whitespace();
  