Track async state in parser.

pkg/front_end/lib/src/fasta/parser/top_level_parser.dart

Index: pkg/front_end/lib/src/fasta/parser/top_level_parser.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/top_level_parser.dart b/pkg/front_end/lib/src/fasta/parser/top_level_parser.dart
index 3e1166fa46f9546fec9c2d3bf5b697f38f966349..27f7e36a4e1fd7e5307ac78049b451a2507a6eab 100644
--- a/pkg/front_end/lib/src/fasta/parser/top_level_parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/top_level_parser.dart
@@ -13,8 +13,7 @@ import 'class_member_parser.dart' show ClassMemberParser;
 /// Parser which only parses top-level elements, but ignores their bodies.
 /// Use [Parser] to parse everything.
 class TopLevelParser extends ClassMemberParser {
-  TopLevelParser(Listener listener, {bool asyncAwaitKeywordsEnabled: false})
-      : super(listener, asyncAwaitKeywordsEnabled: asyncAwaitKeywordsEnabled);
+  TopLevelParser(Listener listener) : super(listener);
 
   Token parseClassBody(Token token) => skipClassBody(token);
 }