cleanup fasta token classes

pkg/front_end/lib/src/fasta/scanner/token.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.scanner.token;
 
 import '../../scanner/token.dart' as analyzer;
 import '../../scanner/token.dart' show Token, TokenType;
 
 import 'token_constants.dart' show IDENTIFIER_TOKEN;
 
 import 'string_canonicalizer.dart';
 
 /**
- * A [SymbolToken] represents the symbol in its precedence info.
- * Also used for end of file with EOF_INFO.
- */
-class SymbolToken extends analyzer.TokenWithComment {
-  SymbolToken(TokenType type, int offset,
-      [analyzer.CommentToken precedingComments])
-      : super(type, offset, precedingComments);
-
-  factory SymbolToken.eof(int charOffset,
-      [analyzer.CommentToken precedingComments]) {
-    var eof =
-        new SyntheticSymbolToken(TokenType.EOF, charOffset, precedingComments);
-    // EOF points to itself so there's always infinite look-ahead.
-    eof.previous = eof;
-    eof.next = eof;
-    return eof;
-  }
-
-  @override
-  String get lexeme => type.value;
-
-  @override
-  String toString() => "SymbolToken(${isEof ? '-eof-' : lexeme})";
-
-  @override
-  Token copy() => isEof
-      ? new SymbolToken.eof(charOffset, precedingComments)
-      : new SymbolToken(type, charOffset, precedingComments);
-}
-
-/**
- * A [SyntheticSymbolToken] represents the symbol in its precedence info
- * which does not exist in the original source.
- * For example, if the scanner finds '(' missing a ')'
- * then it will insert an synthetic ')'.
- */
-class SyntheticSymbolToken extends SymbolToken {
-  SyntheticSymbolToken(TokenType type, int charOffset,
-      [analyzer.CommentToken precedingComments])
-      : super(type, charOffset, precedingComments);
-
-  @override
-  int get length => 0;
-
-  @override
-  Token copy() => isEof
-      ? new SymbolToken.eof(charOffset, precedingComments)
-      : new SyntheticSymbolToken(type, charOffset, precedingComments);
-}
-
-/**
- * A [BeginGroupToken] represents a symbol that may be the beginning of
- * a pair of brackets, i.e., ( { [ < or ${
- * The [endGroup] token points to the matching closing bracket in case
- * it can be identified during scanning.
- */
-class BeginGroupToken extends SymbolToken
-    implements analyzer.BeginTokenWithComment {
-  Token endGroup;
-
-  BeginGroupToken(TokenType type, int charOffset,
-      [analyzer.CommentToken precedingComments])
-      : super(type, charOffset, precedingComments);
-
-  @override
-  analyzer.Token get endToken => endGroup;
-
-  @override
-  void set endToken(analyzer.Token token) {
-    endGroup = token;
-  }
-
-  @override
-  Token copy() => new BeginGroupToken(type, charOffset, precedingComments);
-}
-
-/**
  * A String-valued token. Represents identifiers, string literals,
  * number literals, comments, and error tokens, using the corresponding
  * precedence info.
  */
 class StringToken extends analyzer.TokenWithComment
     implements analyzer.StringTokenWithComment {
   /**
    * The length threshold above which substring tokens are computed lazily.
    *
    * For string tokens that are substrings of the program source, the actual
@@ skipping 287 matching lines @@
       identical(value, "<=") ||
       identical(value, "<") ||
       identical(value, "&") ||
       identical(value, "^") ||
       identical(value, "|");
 }
 
 bool isTernaryOperator(String value) => identical(value, "[]=");
 
 bool isMinusOperator(String value) => identical(value, "-");