Hook for overriding the ContextManager and some code clean-up (with more to follow)

pkg/analysis_server/test/analysis/get_errors_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.analysis.get_errors;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analysis_server/src/protocol.dart';
@@ skipping 81 matching lines @@
 main() {
   print(42)
 }
 ''');
     // handle the request synchronously
     Request request = _createGetErrorsRequest();
     server.handleRequest(request);
     // remove context, causes sending an "invalid file" error
     {
       Folder projectFolder = resourceProvider.getResource(projectPath);
-      server.contextDirectoryManager.removeContext(projectFolder);
+      server.contextManager.removeContext(projectFolder);
     }
     // wait for an error response
     return serverChannel.waitForResponse(request).then((Response response) {
       expect(response.error, isNotNull);
       expect(response.error.code, RequestErrorCode.GET_ERRORS_INVALID_FILE);
     });
   }
 
   Future _checkInvalid(String file) {
     Request request = _createGetErrorsRequest();
     return serverChannel.sendRequest(request).then((Response response) {
       expect(response.error, isNotNull);
       expect(response.error.code, RequestErrorCode.GET_ERRORS_INVALID_FILE);
     });
   }
 
   Request _createGetErrorsRequest() {
     return new AnalysisGetErrorsParams(testFile).toRequest(requestId);
   }
 
   Future<List<AnalysisError>> _getErrors(String file) {
     Request request = _createGetErrorsRequest();
     return serverChannel.sendRequest(request).then((Response response) {
       return new AnalysisGetErrorsResult.fromResponse(response).errors;
     });
   }
 }