Generate constants in server as we do in plugin

pkg/analysis_server/test/domain_server_test.dart

Index: pkg/analysis_server/test/domain_server_test.dart
diff --git a/pkg/analysis_server/test/domain_server_test.dart b/pkg/analysis_server/test/domain_server_test.dart
index a6a867414a482fd0b000e166934bbf84e0a1edf9..f9c7cec2bc33f048ba1cc8961b8cd9f535f41bed 100644
--- a/pkg/analysis_server/test/domain_server_test.dart
+++ b/pkg/analysis_server/test/domain_server_test.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/protocol/protocol.dart';
+import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
@@ -52,7 +53,7 @@ main() {
 
     group('setSubscriptions', () {
       test('invalid service name', () {
-        Request request = new Request('0', SERVER_SET_SUBSCRIPTIONS, {
+        Request request = new Request('0', SERVER_REQUEST_SET_SUBSCRIPTIONS, {
           SUBSCRIPTIONS: ['noSuchService']
         });
         var response = handler.handleRequest(request);