add enableAsync to analysis option file flags

pkg/analysis_server/lib/plugin/protocol/generated_protocol.dart

 // Copyright (c) 2014, 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.
 //
 // This file has been automatically generated.  Please do not edit it manually.
 // To regenerate the file, use the script
 // "pkg/analysis_server/tool/spec/generate_files".
 
 part of analysis_server.plugin.protocol.protocol;
 
@@ skipping 8245 matching lines @@
 
   bool _enableSuperMixins;
 
   bool _generateDart2jsHints;
 
   bool _generateHints;
 
   bool _generateLints;
 
   /**
-   * Deprecated: this feature is always enabled.
-   *
    * True if the client wants to enable support for the proposed async feature.
    */
   bool get enableAsync => _enableAsync;
 
   /**
-   * Deprecated: this feature is always enabled.
-   *
    * True if the client wants to enable support for the proposed async feature.
    */
   void set enableAsync(bool value) {
     this._enableAsync = value;
   }
 
   /**
    * Deprecated: this feature is always enabled.
    *
    * True if the client wants to enable support for the proposed deferred
@@ skipping 8603 matching lines @@
     return false;
   }
 
   @override
   int get hashCode {
     int hash = 0;
     hash = JenkinsSmiHash.combine(hash, newName.hashCode);
     return JenkinsSmiHash.finish(hash);
   }
 }