anchor.diff:  
     Token parseOperatorName(Token token) {
       assert(optional('operator', token));
  -    if (isUserDefinableOperator(token.next.stringValue)) {
  +    if (token.next.isUserDefinableOperator) {
         Token operator = token;
         token = token.next;
         listener.handleOperatorName(operator, token);
  
positive.code:         SyntheticStringToken,
          SyntheticToken,
          TokenType;
  
  import '../scanner/token.dart' show isUserDefinableOperator;
  
  import '../scanner/token_constants.dart'
      show
  
negative.code:     Token hashToken = token;
      listener.beginLiteralSymbol(hashToken);
      token = token.next;
      if (token.isUserDefinableOperator) {
        listener.handleOperator(token);
        listener.endLiteralSymbol(hashToken, 1);
        return token.next;
  