cleanup fasta token classes

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

Index: pkg/front_end/lib/src/scanner/scanner.dart
diff --git a/pkg/front_end/lib/src/scanner/scanner.dart b/pkg/front_end/lib/src/scanner/scanner.dart
index 28590b40472762c8ef04898c5092ebce6a97ccd2..f2c8e3b001224c418f4f30b0fbcac38c92549003 100644
--- a/pkg/front_end/lib/src/scanner/scanner.dart
+++ b/pkg/front_end/lib/src/scanner/scanner.dart
@@ -209,8 +209,7 @@ abstract class Scanner {
    * character [_reader].
    */
   Scanner.create(this._reader) {
-    _tokens = new Token(TokenType.EOF, -1);
-    _tokens.setNext(_tokens);
+    _tokens = new Token.eof(-1);
     _tail = _tokens;
     _tokenStart = -1;
     _lineStarts.add(0);
@@ -545,10 +544,9 @@ abstract class Scanner {
   void _appendEofToken() {
     Token eofToken;
     if (_firstComment == null) {
-      eofToken = new Token(TokenType.EOF, _reader.offset + 1);
+      eofToken = new Token.eof(_reader.offset + 1);
     } else {
-      eofToken = new TokenWithComment(
-          TokenType.EOF, _reader.offset + 1, _firstComment);
+      eofToken = new Token.eof(_reader.offset + 1, _firstComment);
       _firstComment = null;
       _lastComment = null;
     }