Make server use the common protocol classes

pkg/analysis_server/test/integration/analysis/get_errors_nonStandard_sdk.dart

 // Copyright (c) 2016, 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.
 
 import 'dart:async';
 import 'dart:io';
 
-import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analyzer/src/generated/sdk.dart';
+import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../../mock_sdk.dart';
 import '../support/integration_tests.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(AnalysisDomainGetErrorsTest);
@@ skipping 66 matching lines @@
 import 'dart:fake';
 ''';
     writeFile(pathname, text);
     standardAnalysisSetup();
     await analysisFinished;
     List<AnalysisError> errors = currentAnalysisErrors[pathname];
     expect(errors, hasLength(1));
     expect(errors[0].code, 'unused_import');
   }
 }