Generate constants in server as we do in plugin

pkg/analysis_server/test/domain_server_test.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.
 
 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';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:plugin/manager.dart';
 import 'package:test/test.dart';
@@ skipping 29 matching lines @@
       expect(
           response.toJson(),
           equals({
             Response.ID: '0',
             Response.RESULT: {VERSION: AnalysisServer.VERSION}
           }));
     });
 
     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);
         expect(response, isResponseFailure('0'));
       });
 
       test('success', () {
         expect(server.serverServices, isEmpty);
         // send request
         Request request =
@@ skipping 10 matching lines @@
       expect(server.running, isTrue);
       // send request
       var request = new ServerShutdownParams().toRequest('0');
       var response = handler.handleRequest(request);
       expect(response, isResponseSuccess('0'));
       // server is down
       expect(server.running, isFalse);
     });
   });
 }