fasta scanner recovery and error code translation improvements

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 'keyword.dart' show Keyword;
 
 import 'precedence.dart'
     show
         AS_INFO,
         BAD_INPUT_INFO,
         EOF_INFO,
         IDENTIFIER_INFO,
         IS_INFO,
         KEYWORD_INFO,
-        MULTI_LINE_COMMENT_INFO,
-        SINGLE_LINE_COMMENT_INFO,
         PrecedenceInfo;
 
 import 'token_constants.dart' show IDENTIFIER_TOKEN;
 
 import 'string_canonicalizer.dart';
 
 /**
  * A token that doubles as a linked list.
  */
 abstract class Token implements analyzer.TokenWithComment {
@@ skipping 220 matching lines @@
 
 /**
  * A [SymbolToken] represents the symbol in its precedence info.
  * Also used for end of file with EOF_INFO.
  */
 class SymbolToken extends Token {
   final PrecedenceInfo info;
 
   SymbolToken(this.info, int charOffset) : super(charOffset);
 
+  SymbolToken.eof(int charOffset)
+      : info = EOF_INFO,
+        super(charOffset) {
+    // EOF points to itself so there's always infinite look-ahead.
+    previousToken = this;
+    next = this;
+  }
+
   String get lexeme => info.value;
 
   String get stringValue => info.value;
 
   bool isIdentifier() => false;
 
-  String toString() => "SymbolToken($lexeme)";
+  String toString() => "SymbolToken(${info == EOF_INFO ? '-eof-' : lexeme})";
 
   bool get isEof => info == EOF_INFO;
 
   @override
   Token copyWithoutComments() => new SymbolToken(info, charOffset);
 }
 
 /**
  * A [BeginGroupToken] represents a symbol that may be the beginning of
  * a pair of brackets, i.e., ( { [ < or ${
@@ skipping 350 matching lines @@
       identical(value, "<=") ||
       identical(value, "<") ||
       identical(value, "&") ||
       identical(value, "^") ||
       identical(value, "|");
 }
 
 bool isTernaryOperator(String value) => identical(value, "[]=");
 
 bool isMinusOperator(String value) => identical(value, "-");