Remove more references to the old plugin system

pkg/analysis_server/test/analysis_server_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.
 
 import 'dart:async';
 
 import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_constants.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
 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 'mock_sdk.dart';
 import 'mocks.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(AnalysisServerTest);
   });
@@ skipping 49 matching lines @@
         default:
           if (!notificationTypesReceived.add(notificationType)) {
             fail('Notification type $notificationType received more than once');
           }
           break;
       }
     }
   }
 
   void processRequiredPlugins() {
-    List<Plugin> plugins = <Plugin>[];
-    plugins.addAll(AnalysisEngine.instance.requiredPlugins);
-
     ExtensionManager manager = new ExtensionManager();
-    manager.processPlugins(plugins);
+    manager.processPlugins(AnalysisEngine.instance.requiredPlugins);
   }
 
   void setUp() {
     processRequiredPlugins();
     channel = new MockServerChannel();
     resourceProvider = new MemoryResourceProvider();
     // Create an SDK in the mock file system.
     new MockSdk(resourceProvider: resourceProvider);
     packageMapProvider = new MockPackageMapProvider();
     server = new AnalysisServer(
@@ skipping 101 matching lines @@
 
 class EchoHandler implements RequestHandler {
   @override
   Response handleRequest(Request request) {
     if (request.method == 'echo') {
       return new Response(request.id, result: {'echo': true});
     }
     return null;
   }
 }