Move the wire protocol support into the public API

pkg/analysis_server/test/search/element_references_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.search.element_references;
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol.dart';
+import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:unittest/unittest.dart';
 
 import '../utils.dart';
 import 'abstract_search_domain.dart';
 
 main() {
   initializeTestEnvironment();
   defineReflectiveTests(ElementReferencesTest);
@@ skipping 698 matching lines @@
   print(vvv);
 }
 ''');
     Request request = new SearchFindElementReferencesParams(testFile, 0, false)
         .toRequest('0');
     Response response = await waitResponse(request);
     expect(response.error, isNotNull);
     expect(response.error.code, RequestErrorCode.NO_INDEX_GENERATED);
   }
 }