cleanup fasta token classes

pkg/front_end/lib/src/fasta/source/source_library_builder.dart

 // Copyright (c) 2016, 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.source_library_builder;
 
 import 'package:front_end/src/scanner/token.dart' show Token;
 
-import 'package:front_end/src/fasta/scanner/token.dart' show SymbolToken;
-
 import 'package:kernel/ast.dart' show ProcedureKind;
 
 import '../combinator.dart' show Combinator;
 
 import '../errors.dart' show inputError, internalError;
 
 import '../export.dart' show Export;
 
 import '../import.dart' show Import;
 
@@ skipping 172 matching lines @@
     for (int i = 0; i < namesOffsetsAndInitializers.length; i += 4) {
       String name = namesOffsetsAndInitializers[i];
       int charOffset = namesOffsetsAndInitializers[i + 1];
       Token initializer;
       if (type == null) {
         initializer = namesOffsetsAndInitializers[i + 2];
         Token afterInitializer = namesOffsetsAndInitializers[i + 3];
         // TODO(paulberry): figure out a way to do this without using
         // Token.previous.
         afterInitializer?.previous
-            ?.setNext(new SymbolToken.eof(afterInitializer.offset));
+            ?.setNext(new Token.eof(afterInitializer.offset));
       }
       addField(metadata, modifiers, type, name, charOffset, initializer);
     }
   }
 
   void addProcedure(
       List<MetadataBuilder> metadata,
       int modifiers,
       T returnType,
       String name,
@@ skipping 353 matching lines @@
   /// synthesize type variables on the factory matching the class'.
   void addFactoryDeclaration(
       ProcedureBuilder procedure, DeclarationBuilder<T> factoryDeclaration) {
     factoryDeclarations[procedure] = factoryDeclaration;
   }
 
   Scope toScope(Scope parent) {
     return new Scope(members, setters, parent, isModifiable: false);
   }
 }