Revert server test extension manager "fix" [TBR].

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.
 
 library test.analysis_server;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
@@ skipping 105 matching lines @@
       expect(fooContext.getKindOf(barSource), SourceKind.UNKNOWN);
       expect(barContext.getKindOf(fooSource), SourceKind.UNKNOWN);
       expect(barContext.getKindOf(barSource), SourceKind.LIBRARY);
     });
   }
 
   void setUp() {
     channel = new MockServerChannel();
     resourceProvider = new MemoryResourceProvider();
     packageMapProvider = new MockPackageMapProvider();
-
+    ExtensionManager manager = new ExtensionManager();
     ServerPlugin serverPlugin = new ServerPlugin();
-
-    // Defer to the extension manager in AE for plugin registration.
-    AnalysisEngine.instance.userDefinedPlugins = [serverPlugin];
-    // Force registration.
-    AnalysisEngine.instance.taskManager;
-
+    manager.processPlugins([serverPlugin]);
     server = new AnalysisServer(
         channel,
         resourceProvider,
         packageMapProvider,
         null,
         serverPlugin,
         new AnalysisServerOptions(),
         new MockSdk(),
         InstrumentationService.NULL_SERVICE,
         rethrowExceptions: true);
@@ skipping 375 matching lines @@
   _MockServerOperation(this.context);
 
   @override
   ServerOperationPriority get priority => ServerOperationPriority.ANALYSIS;
 
   @override
   void perform(AnalysisServer server) {
     isComplete = true;
   }
 }