Track async state in parser.

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

Index: pkg/front_end/lib/src/fasta/source/diet_parser.dart
diff --git a/pkg/front_end/lib/src/fasta/source/diet_parser.dart b/pkg/front_end/lib/src/fasta/source/diet_parser.dart
index 35b9da2b44bfd414bf077797cf6df7e07bde2950..82251320e134808dd493a41be37673ad3c933444 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_parser.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_parser.dart
@@ -16,8 +16,7 @@ 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);