Change error code for server shutting down

See https://github.com/Microsoft/language-server-protocol/issues/684#issuecomment-477215334.

Change-Id: I9e45dd27ea914af8bc3b936e9885c113211c50ce
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/102361
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Danny Tuppeny <dantup@google.com>
diff --git a/pkg/analysis_server/lib/src/lsp/constants.dart b/pkg/analysis_server/lib/src/lsp/constants.dart
index 2c4999c..aaf762f 100644
--- a/pkg/analysis_server/lib/src/lsp/constants.dart
+++ b/pkg/analysis_server/lib/src/lsp/constants.dart
@@ -41,7 +41,6 @@
   static const FileHasErrors = const ErrorCodes(-32008);
   static const ClientFailedToApplyEdit = const ErrorCodes(-32009);
   static const RenameNotValid = const ErrorCodes(-32010);
-  static const ServerShuttingDown = const ErrorCodes(-32011);
 
   /// An error raised when the server detects that the server and client are out
   /// of sync and cannot recover. For example if a textDocument/didChange notification
diff --git a/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart b/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart
index cd79433..bf4600e 100644
--- a/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart
+++ b/pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart
@@ -141,7 +141,7 @@
     if (message is! RequestMessage) {
       return success();
     }
-    return failure(ServerErrorCodes.ServerShuttingDown,
+    return failure(ErrorCodes.InvalidRequest,
         'Unable to handle ${message.method} after shutdown request');
   }
 }