Minor fixes.

pkg/front_end/lib/src/fasta/analyzer/ast_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.analyzer.ast_builder;
 
 import 'package:front_end/src/fasta/scanner/token.dart'
     show BeginGroupToken, Token;
 
 import 'package:analyzer/analyzer.dart';
 
 import 'package:analyzer/dart/ast/token.dart' as analyzer show Token;
 
 import 'package:analyzer/dart/element/element.dart' show Element;
 
 import 'package:analyzer/dart/ast/ast_factory.dart' show AstFactory;
 
 import 'package:analyzer/dart/ast/standard_ast_factory.dart' as standard;
 
 import 'package:kernel/ast.dart' show AsyncMarker;
 
 import '../errors.dart' show internalError;
 
 import '../source/scope_listener.dart'
     show JumpTargetKind, NullValue, Scope, ScopeListener;
 
 import '../kernel/kernel_builder.dart'
     show Builder, KernelLibraryBuilder, ProcedureBuilder;
 
+import '../parser/parser.dart' show optional;
+
 import '../quote.dart';
 
 import '../source/outline_builder.dart' show asyncMarkerFromTokens;
 
 import 'element_store.dart'
     show
         AnalyzerLocalVariableElemment,
         AnalyzerParameterElement,
         ElementStore,
         KernelClassElement;
@@ skipping 749 matching lines @@
       withClause = ast.withClause(
           toAnalyzerToken(supertype.withKeyword), supertype.mixinTypes);
     } else {
       internalError('Unexpected kind of supertype ${supertype.runtimeType}');
     }
     TypeParameterList typeParameters = pop();
     SimpleIdentifier name = pop();
     Token classKeyword;
     // TODO(paulberry,ahe): This is a hack.  The parser should give us the class
     // keyword.
-    if (identical(beginToken.value, 'abstract')) {
+    if (optional('abstract', beginToken)) {
       classKeyword = beginToken.next;
     } else {
       classKeyword = beginToken;
     }
     var modifiers = pop();
     assert(modifiers == null); // TODO(paulberry)
     analyzer.Token abstractKeyword;
     List<Annotation> metadata = pop();
     Comment comment = null; // TODO(paulberry)
     push(ast.classDeclaration(
@@ skipping 155 matching lines @@
 /// [ClassDeclaration] or [ClassTypeAlias] object.
 class _MixinApplication {
   final TypeName supertype;
 
   final Token withKeyword;
 
   final List<TypeName> mixinTypes;
 
   _MixinApplication(this.supertype, this.withKeyword, this.mixinTypes);
 }