Separate the API's used by ContextManager.

pkg/analysis_server/test/analysis/get_navigation_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_navigation;
 
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
@@ skipping 64 matching lines @@
   print(test);
 }
 ''');
     // handle the request synchronously
     Request request =
         _createGetNavigationRequest(testFile, testCode.indexOf('test);'), 0);
     server.handleRequest(request);
     // remove context, causes sending an "invalid file" error
     {
       Folder projectFolder = resourceProvider.getResource(projectPath);
-      server.contextManager.removeContext(projectFolder);
+      server.contextManager.callbacks.removeContext(projectFolder, <String>[]);
     }
     // wait for an error response
     Response response = await serverChannel.waitForResponse(request);
     expect(response.error, isNotNull);
     expect(response.error.code, RequestErrorCode.GET_NAVIGATION_INVALID_FILE);
   }
 
   _checkInvalid(String file, int offset, int length) async {
     Request request = _createGetNavigationRequest(file, offset, length);
     Response response = await serverChannel.sendRequest(request);
     expect(response.error, isNotNull);
     expect(response.error.code, RequestErrorCode.GET_NAVIGATION_INVALID_FILE);
   }
 
   Request _createGetNavigationRequest(String file, int offset, int length) {
     return new AnalysisGetNavigationParams(file, offset, length)
         .toRequest(requestId);
   }
 
   _getNavigation(String file, int offset, int length) async {
     Request request = _createGetNavigationRequest(file, offset, length);
     Response response = await serverChannel.sendRequest(request);
     AnalysisGetNavigationResult result =
         new AnalysisGetNavigationResult.fromResponse(response);
     targetFiles = result.files;
     targets = result.targets;
     regions = result.regions;
   }
 }