add enableAsync to analysis option file flags

pkg/analysis_server/lib/src/status/get_handler.dart

Index: pkg/analysis_server/lib/src/status/get_handler.dart
diff --git a/pkg/analysis_server/lib/src/status/get_handler.dart b/pkg/analysis_server/lib/src/status/get_handler.dart
index 0f4fc1590013186061e4117e852c0e6f98d9da2d..72600138074b052053ce079b98026caab8214c32 100644
--- a/pkg/analysis_server/lib/src/status/get_handler.dart
+++ b/pkg/analysis_server/lib/src/status/get_handler.dart
@@ -1252,6 +1252,7 @@ class GetHandler {
           _writeOption(
               buffer, 'Analyze functon bodies', options.analyzeFunctionBodies);
           _writeOption(buffer, 'Cache size', options.cacheSize);
+          _writeOption(buffer, 'Enable async support', options.enableAsync);
           _writeOption(
               buffer, 'Enable generic methods', options.enableGenericMethods);
           _writeOption(buffer, 'Enable strict call checks',