Remove more references to the old plugin system

pkg/analysis_server/test/context_manager_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.context.directory.manager;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/context_manager.dart';
 import 'package:analysis_server/src/plugin/notification_manager.dart';
@@ skipping 14 matching lines @@
 import 'package:analyzer/src/generated/source_io.dart';
 import 'package:analyzer/src/services/lint.dart';
 import 'package:analyzer/src/summary/summary_file_builder.dart';
 import 'package:analyzer/src/util/glob.dart';
 import 'package:front_end/src/base/performace_logger.dart';
 import 'package:front_end/src/byte_store/byte_store.dart';
 import 'package:linter/src/rules.dart';
 import 'package:linter/src/rules/avoid_as.dart';
 import 'package:path/path.dart' as path;
 import 'package:plugin/manager.dart';
-import 'package:plugin/plugin.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:watcher/watcher.dart';
 
 import 'mock_sdk.dart';
 import 'mocks.dart';
 import 'src/plugin/plugin_manager_test.dart';
 
 main() {
   defineReflectiveSuite(() {
@@ skipping 1716 matching lines @@
     return filePath;
   }
 
   String newFolder(List<String> pathComponents) {
     String folderPath = path.posix.joinAll(pathComponents);
     resourceProvider.newFolder(folderPath);
     return folderPath;
   }
 
   void processRequiredPlugins() {
-    List<Plugin> plugins = <Plugin>[];
-    plugins.addAll(AnalysisEngine.instance.requiredPlugins);
     ExtensionManager manager = new ExtensionManager();
-    manager.processPlugins(plugins);
+    manager.processPlugins(AnalysisEngine.instance.requiredPlugins);
 
     registerLintRules();
   }
 
   UriResolver providePackageResolver(Folder folder) => packageResolver;
 
   void setUp() {
     processRequiredPlugins();
     resourceProvider = new MemoryResourceProvider();
     resourceProvider.newFolder(projPath);
@@ skipping 900 matching lines @@
 class TestUriResolver extends UriResolver {
   Map<Uri, Source> uriMap;
 
   TestUriResolver(this.uriMap);
 
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     return uriMap[uri];
   }
 }