cleanup fasta token classes

pkg/front_end/test/fasta/parser/token_stream_rewriter_test.dart

 // Copyright (c) 2017, 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.
 
 import 'package:front_end/src/fasta/parser/token_stream_rewriter.dart';
 import 'package:front_end/src/fasta/scanner/token.dart';
-import 'package:front_end/src/scanner/token.dart' show Token, TokenType;
+import 'package:front_end/src/scanner/token.dart'
+    show BeginToken, Token, TokenType;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TokenStreamRewriterTest_NoPrevious);
     defineReflectiveTests(TokenStreamRewriterTest_UsingPrevious);
   });
 }
 
@@ skipping 79 matching lines @@
     rewriter.insertTokenBefore(d, e);
     expect(c.next, same(d));
     expect(d.next, same(e));
   }
 
   /// Links together the given [tokens] and adds an EOF token to the end of the
   /// token stream.
   ///
   /// The EOF token is returned.
   Token _link(Iterable<Token> tokens) {
-    Token head = new SymbolToken.eof(-1);
+    Token head = new Token.eof(-1);
     if (!setPrevious) head.previous = null;
     for (var token in tokens) {
       head.next = token;
       if (setPrevious) token.previous = head;
       head = token;
     }
     int eofOffset = head.charOffset + head.lexeme.length;
     if (eofOffset < 0) eofOffset = 0;
-    Token eof = new SymbolToken.eof(eofOffset);
+    Token eof = new Token.eof(eofOffset);
     if (!setPrevious) eof.previous = null;
     head.next = eof;
     if (setPrevious) eof.previous = head;
     return eof;
   }
 
-  BeginGroupToken _makeBeginGroupToken(int charOffset) {
-    return new BeginGroupToken(TokenType.OPEN_PAREN, charOffset);
+  BeginToken _makeBeginGroupToken(int charOffset) {
+    return new BeginToken(TokenType.OPEN_PAREN, charOffset);
   }
 
   StringToken _makeToken(int charOffset, String text) {
     return new StringToken.fromString(null, text, charOffset);
   }
 }
 
 /// Concrete implementation of [TokenStreamRewriterTest] in which
 /// [Token.previous] values are set to null.
 ///
 /// This forces [TokenStreamRewriter] to use its more complex heursitc for
 /// finding previous tokens.
 @reflectiveTest
 class TokenStreamRewriterTest_NoPrevious extends TokenStreamRewriterTest {
   bool get setPrevious => false;
 }
 
 /// Concrete implementation of [TokenStreamRewriterTest] in which
 /// [Token.previous] values are set to non-null.
 ///
 /// Since [TokenStreamRewriter] makes use of [Token.previous] when it can,
 /// these tests do not exercise the more complex heuristics for finding previous
 /// tokens.
 @reflectiveTest
 class TokenStreamRewriterTest_UsingPrevious extends TokenStreamRewriterTest {
   bool get setPrevious => true;
 }