Clean-up the registration of plugins

pkg/analysis_server/test/services/correction/assist_test.dart

Index: pkg/analysis_server/test/services/correction/assist_test.dart
diff --git a/pkg/analysis_server/test/services/correction/assist_test.dart b/pkg/analysis_server/test/services/correction/assist_test.dart
index 48e806877a6c2c559df078881996d6760bb0f56b..22bfe52c92e31a6cc8f973ee30bc74f61e08409c 100644
--- a/pkg/analysis_server/test/services/correction/assist_test.dart
+++ b/pkg/analysis_server/test/services/correction/assist_test.dart
@@ -10,8 +10,10 @@ import 'package:analysis_server/plugin/edit/assist/assist_core.dart';
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
 import 'package:analysis_server/src/services/correction/assist.dart';
+import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:plugin/manager.dart';
+import 'package:plugin/plugin.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 import 'package:unittest/unittest.dart';
 
@@ -99,13 +101,21 @@ class AssistProcessorTest extends AbstractSingleUnitTest {
     }).toList();
   }
 
+  void processRequiredPlugins() {
+    plugin = new ServerPlugin();
+
+    List<Plugin> plugins = <Plugin>[];
+    plugins.addAll(AnalysisEngine.instance.requiredPlugins);
+    plugins.add(plugin);
+
+    ExtensionManager manager = new ExtensionManager();
+    manager.processPlugins(plugins);
+  }
+
   void setUp() {
     super.setUp();
     offset = 0;
     length = 0;
-    ExtensionManager manager = new ExtensionManager();
-    plugin = new ServerPlugin();
-    manager.processPlugins([plugin]);
   }
 
   test_addTypeAnnotation_BAD_privateType_closureParameter() async {