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

pkg/analysis_server/test/socket_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.
 
 library test.socket.server;
 
 import 'dart:async';
 
 import 'mocks.dart';
 
@@ skipping 33 matching lines @@
     MockServerChannel channel1 = new MockServerChannel();
     MockServerChannel channel2 = new MockServerChannel();
     server.createAnalysisServer(channel1);
     expect(channel1.notificationsReceived[0].event, SERVER_CONNECTED);
     server.createAnalysisServer(channel2);
     channel1.expectMsgCount(notificationCount: 1);
     channel2.expectMsgCount(responseCount: 1);
     expect(channel2.responsesReceived[0].id, equals(''));
     expect(channel2.responsesReceived[0].error, isNotNull);
     expect(channel2.responsesReceived[0].error.code, equals(
-        RequestError.CODE_SERVER_ALREADY_STARTED));
+        RequestErrorCode.SERVER_ALREADY_STARTED));
     channel2.sendRequest(new ServerShutdownParams().toRequest('0')).then(
         (Response response) {
       expect(response.id, equals('0'));
       expect(response.error, isNotNull);
       expect(response.error.code, equals(
-          RequestError.CODE_SERVER_ALREADY_STARTED));
+          RequestErrorCode.SERVER_ALREADY_STARTED));
       channel2.expectMsgCount(responseCount: 2);
     });
   }
 }