Temporarily move plugin support

pkg/analyzer/test/plugin/plugin_impl_test.dart

 // Copyright (c) 2015, 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.operation;
 
-import 'package:analysis_server/plugin/plugin.dart';
-import 'package:analysis_server/src/plugin/plugin_impl.dart';
+import 'package:analyzer/plugin/plugin.dart';
+import 'package:analyzer/src/plugin/plugin_impl.dart';
 import 'package:unittest/unittest.dart';
 
 main() {
   groupSep = ' | ';
 
   group('ExtensionManager', () {
     test('processPlugins', () {
       TestPlugin plugin1 = new TestPlugin('plugin1');
       TestPlugin plugin2 = new TestPlugin('plugin1');
       ExtensionManager manager = new ExtensionManager();
@@ skipping 146 matching lines @@
   @override
   void registerExtensionPoints(RegisterExtensionPoint register) {
     extensionPointsRegistered = true;
   }
 
   @override
   void registerExtensions(RegisterExtension register) {
     extensionsRegistered = true;
   }
 }