Temporarily move plugin support

pkg/analysis_server/lib/src/plugin/server_plugin.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.server_plugin;
 
-import 'package:analysis_server/plugin/plugin.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analysis_server/src/domain_completion.dart';
 import 'package:analysis_server/src/domain_execution.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analysis_server/src/search/search_domain.dart';
+import 'package:analyzer/plugin/plugin.dart';
 
 /**
  * A function that will create a request handler that can be used by the given
  * [server].
- *
- * TODO(brianwilkerson) Move this into 'protocol.dart'.
  */
 typedef RequestHandler RequestHandlerFactory(AnalysisServer server);
 
 /**
  * A plugin that defines the extension points and extensions that are inherently
  * defined by the analysis server.
  */
 class ServerPlugin implements Plugin {
   /**
    * The simple identifier of the extension point that allows plugins to
@@ skipping 61 matching lines @@
    * valid domain.
    */
   void _validateDomainExtension(Object extension) {
     if (extension is! RequestHandlerFactory) {
       String id = domainExtensionPoint.uniqueIdentifier;
       throw new ExtensionError(
           'Extensions to $id must be a RequestHandlerFactory');
     }
   }
 }