Temporarily move plugin support

pkg/analyzer/lib/src/plugin/plugin_impl.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 analysis_server.src.plugin.plugin_impl;
+library analyzer.src.plugin.plugin_impl;
 
 import 'dart:collection';
 
-import 'package:analysis_server/plugin/plugin.dart';
+import 'package:analyzer/plugin/plugin.dart';
 
 /**
  * An object that manages the extension points for a single instance of the
  * analysis server.
  */
 class ExtensionManager {
   /**
    * A table mapping the id's of extension points to the corresponding
    * extension points.
    */
@@ skipping 96 matching lines @@
    * Validate that the given [extension] is appropriate for this extension
    * point, and if it is then add it to the list of registered exceptions.
    */
   void add(Object extension) {
     if (validateExtension != null) {
       validateExtension(extension);
     }
     _extensions.add(extension);
   }
 }