cleanup fasta token classes

pkg/compiler/lib/src/native/resolver.dart

 // Copyright (c) 2014, 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/scanner.dart'
-    show BeginGroupToken, StringToken, Token;
+import 'package:front_end/src/fasta/scanner.dart' show StringToken, Token;
 import 'package:front_end/src/fasta/scanner.dart' as Tokens show EOF_TOKEN;
+import 'package:front_end/src/scanner/token.dart' show BeginToken;
 
 import '../common.dart';
 import '../common_elements.dart' show CommonElements, ElementEnvironment;
 import '../common/backend_api.dart';
 import '../common/resolution.dart';
 import '../compiler.dart' show Compiler;
 import '../constants/values.dart';
 import '../elements/elements.dart'
     show
         ClassElement,
@@ skipping 540 matching lines @@
     // will slightly increase parse time and size and cause compiler errors and
     // warnings to me emitted in more unused code.
 
     // An alternative to this code is to extend the API of ClassElement to
     // expose the name of the extended element.
 
     // Pattern match the above cases in the token stream.
     //  [abstract] class X extends [id.]* id
 
     Token skipTypeParameters(Token token) {
-      BeginGroupToken beginGroupToken = token;
+      BeginToken beginGroupToken = token;
       Token endToken = beginGroupToken.endGroup;
       return endToken.next;
       //for (;;) {
       //  token = token.next;
       //  if (token.stringValue == '>') return token.next;
       //  if (token.stringValue == '<') return skipTypeParameters(token);
       //}
     }
 
     String scanForExtendsName(Token token) {
@@ skipping 36 matching lines @@
 
   Iterable<ConstantValue> fields = constructedObject.fields.values;
   // TODO(sra): Better validation of the constant.
   if (fields.length != 1 || fields.single is! StringConstantValue) {
     throw new SpannableAssertionFailure(
         spannable, 'Annotations needs one string: ${value.toStructuredText()}');
   }
   StringConstantValue specStringConstant = fields.single;
   return specStringConstant.primitiveValue;
 }