fasta scanner recovery and error code translation improvements

pkg/front_end/lib/src/fasta/scanner/array_based_scanner.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.array_based_scanner;
 
 import 'error_token.dart' show ErrorToken;
 
 import 'keyword.dart' show Keyword;
 
@@ skipping 89 matching lines @@
     appendToken(new KeywordToken(keyword, tokenStart));
   }
 
   void appendEofToken() {
     beginToken();
     discardOpenLt();
     while (!groupingStack.isEmpty) {
       unmatchedBeginGroup(groupingStack.head);
       groupingStack = groupingStack.tail;
     }
-    appendToken(new SymbolToken(EOF_INFO, tokenStart));
-    // EOF points to itself so there's always infinite look-ahead.
-    tail.next = tail;
+    appendToken(new SymbolToken.eof(tokenStart));
   }
 
   /**
    * Notifies scanning a whitespace character. Note that [appendWhiteSpace] is
    * not always invoked for [$SPACE] characters.
    *
    * This method is used by the scanners to track line breaks and create the
    * [lineStarts] map.
    */
   void appendWhiteSpace(int next) {
@@ skipping 192 matching lines @@
    * something which cannot possibly be part of a type parameter/argument
    * list, like the '=' in the above example.
    */
   void discardOpenLt() {
     while (!groupingStack.isEmpty &&
         identical(groupingStack.head.kind, LT_TOKEN)) {
       groupingStack = groupingStack.tail;
     }
   }
 }