Track async state in parser.

pkg/front_end/lib/src/fasta/source/diet_parser.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.diet_parser;
 
 import '../scanner/token.dart' show BeginGroupToken, Token;
 
 import '../parser/class_member_parser.dart' show ClassMemberParser;
 
 import '../parser/error_kind.dart' show ErrorKind;
 
 import '../parser/listener.dart' show Listener;
 
 import '../parser/parser.dart' show optional;
 
 // TODO(ahe): Move this to parser package.
 class DietParser extends ClassMemberParser {
-  DietParser(Listener listener, {bool asyncAwaitKeywordsEnabled: false})
-      : super(listener, asyncAwaitKeywordsEnabled: asyncAwaitKeywordsEnabled);
+  DietParser(Listener listener) : super(listener);
 
   Token parseFormalParameters(Token token, {bool inFunctionType: false}) {
     return skipFormals(token);
   }
 
   Token skipFormals(Token token) {
     listener.beginOptionalFormalParameters(token);
     if (!optional('(', token)) {
       if (optional(';', token)) {
         reportRecoverableError(token, ErrorKind.ExpectedOpenParens, {});
         return token;
       }
       return reportUnrecoverableError(token, ErrorKind.UnexpectedToken)?.next;
     }
     BeginGroupToken beginGroupToken = token;
     Token endToken = beginGroupToken.endGroup;
     listener.endFormalParameters(0, token, endToken);
     return endToken.next;
   }
 }