Generate constants in server as we do in plugin

pkg/analysis_server/lib/src/domain_diagnostic.dart

 // Copyright (c) 2015, 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 'dart:async';
 import 'dart:collection';
 import 'dart:core';
 
 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:analyzer/src/context/cache.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/dart/analysis/driver.dart' as nd;
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_collection.dart';
 import 'package:analyzer/src/task/driver.dart';
 import 'package:analyzer/task/model.dart';
 
 int _workItemCount(AnalysisContextImpl context) {
@@ skipping 76 matching lines @@
     } catch (error) {
       server
           .sendResponse(new Response.debugPortCouldNotBeOpened(request, error));
     }
   }
 
   @override
   Response handleRequest(Request request) {
     try {
       String requestName = request.method;
-      if (requestName == DIAGNOSTIC_GET_DIAGNOSTICS) {
+      if (requestName == DIAGNOSTIC_REQUEST_GET_DIAGNOSTICS) {
         return computeDiagnostics(request);
-      } else if (requestName == DIAGNOSTIC_GET_SERVER_PORT) {
+      } else if (requestName == DIAGNOSTIC_REQUEST_GET_SERVER_PORT) {
         handleGetServerPort(request);
         return Response.DELAYED_RESPONSE;
       }
     } on RequestFailure catch (exception) {
       return exception.response;
     }
     return null;
   }
 }
 
 class MemoryCpuSample {
   final DateTime time;
   final double cpuPercentage;
   final int memoryKB;
 
   MemoryCpuSample(this.time, this.cpuPercentage, this.memoryKB);
 }