Make index provisional API.

pkg/analysis_server/lib/src/provisional/index/index.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.
 
 /**
  * Support for client code that extends the analysis server by adding new index
  * contributors.
  *
  * Plugins can register index contributors. The registered contributors will be
  * used to contribute relationships to the index when the analysis of a file has
@@ skipping 12 matching lines @@
  *     void registerExtensions(RegisterExtension registerExtension) {
  *       ...
  *       registerExtension(
  *           INDEX_CONTRIBUTOR_EXTENSION_POINT_ID,
  *           new MyIndexContributor());
  *       ...
  *     }
  */
 library analysis_server.plugin.index.index;
 
-import 'package:analysis_server/plugin/index/index_core.dart';
 import 'package:analysis_server/src/plugin/server_plugin.dart';
+import 'package:analysis_server/src/provisional/index/index_core.dart';
 import 'package:plugin/plugin.dart';
 
 /**
  * The identifier of the extension point that allows plugins to register index
  * contributors. The object used as an extension must be an [IndexContributor].
  */
 final String INDEX_CONTRIBUTOR_EXTENSION_POINT_ID = Plugin.join(
     ServerPlugin.UNIQUE_IDENTIFIER,
     ServerPlugin.INDEX_CONTRIBUTOR_EXTENSION_POINT);