In the analysis server API, change RequestError.code to an enum.

pkg/analysis_server/test/analysis/get_errors_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.
 
 library test.analysis.get_errors;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analysis_server/src/protocol.dart';
@@ skipping 95 matching lines @@
     {
       Folder projectFolder = resourceProvider.getResource(projectPath);
       server.contextDirectoryManager.removeContext(projectFolder);
     }
     // wait for an error response
     return serverChannel.waitForResponse(request).then((Response response) {
       var result = new AnalysisGetErrorsResult.fromResponse(response);
       expect(result.errors, isEmpty);
       RequestError error = response.error;
       expect(error, isNotNull);
-      expect(error.code, 'GET_ERRORS_ERROR');
+      expect(error.code, RequestErrorCode.GET_ERRORS_ERROR);
     });
   }
 
   Request _createGetErrorsRequest() {
     return new AnalysisGetErrorsParams(testFile).toRequest(requestId);
   }
 
   Future<List<AnalysisError>> _getErrors(String file) {
     Request request = _createGetErrorsRequest();
     return serverChannel.sendRequest(request).then((Response response) {
       return new AnalysisGetErrorsResult.fromResponse(response).errors;
     });
   }
 }