Make server use the common protocol classes

pkg/analysis_server/test/edit/statement_completion_test.dart

 // Copyright (c) 2017, 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.edit.statement_completion;
-
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
+import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:plugin/manager.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../analysis_abstract.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(StatementCompletionTest);
   });
@@ skipping 101 matching lines @@
   }
 
   _prepareCompletionAt(int offset) async {
     Request request =
         new EditGetStatementCompletionParams(testFile, offset).toRequest('0');
     Response response = await waitResponse(request);
     var result = new EditGetStatementCompletionResult.fromResponse(response);
     change = result.change;
   }
 }