Move the wire protocol support into the public API

pkg/analysis_server/test/domain_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.domain.server;
 
+import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
-import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:plugin/manager.dart';
 import 'package:unittest/unittest.dart';
 
 import 'mock_sdk.dart';
 import 'mocks.dart';
 import 'utils.dart';
 
 main() {
@@ skipping 58 matching lines @@
       expect(server.running, isTrue);
       // send request
       var request = new ServerShutdownParams().toRequest('0');
       var response = handler.handleRequest(request);
       expect(response, isResponseSuccess('0'));
       // server is down
       expect(server.running, isFalse);
     });
   });
 }