Unify the server and plugin versions of the generators

pkg/analysis_server/test/channel/web_socket_channel_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.channel.web_socket;
 
 import 'dart:async';
 
-import 'package:analysis_server/plugin/protocol/protocol.dart';
+import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/src/channel/web_socket_channel.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:test/test.dart';
 
 import '../mocks.dart';
 
 main() {
   group('WebSocketChannel', () {
     setUp(WebSocketChannelTest.setUp);
     test('close', WebSocketChannelTest.close);
@@ skipping 127 matching lines @@
     notificationsReceived = <Notification>[];
 
     // Allow multiple listeners on server side for testing.
     socket.twin.allowMultipleListeners();
 
     server.listen(requestsReceived.add);
     client.responseStream.listen(responsesReceived.add);
     client.notificationStream.listen(notificationsReceived.add);
   }
 }