Generate constants in server as we do in plugin

pkg/analysis_server/test/domain_completion_util.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 'dart:async';
 
 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/constants.dart';
 import 'package:analysis_server/src/domain_completion.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:test/test.dart';
 
 import 'analysis_abstract.dart';
 
@@ skipping 84 matching lines @@
       String id = params.id;
       assertValidId(id);
       replacementOffset = params.replacementOffset;
       replacementLength = params.replacementLength;
       suggestionsDone = params.isLast;
       expect(suggestionsDone, isNotNull);
       suggestions = params.results;
       expect(allSuggestions.containsKey(id), isFalse);
       allSuggestions[id] = params.results;
       _getResultsCompleter(id).complete(null);
-    } else if (notification.event == SERVER_ERROR) {
+    } else if (notification.event == SERVER_NOTIFICATION_ERROR) {
       fail('server error: ${notification.toJson()}');
     }
   }
 
   @override
   void setUp() {
     super.setUp();
     createProject();
     handler = new CompletionDomainHandler(server);
   }
 
   Completer<Null> _getResultsCompleter(String id) {
     return receivedSuggestionsCompleters.putIfAbsent(
         id, () => new Completer<Null>());
   }
 }