Make index provisional API.

pkg/analysis_server/lib/src/services/index/index_store.dart

 // Copyright (c) 2014, 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 services.index_store;
 
-import 'package:analysis_server/plugin/index/index_core.dart';
+import 'package:analysis_server/src/provisional/index/index_core.dart';
 import 'package:analysis_server/src/services/index/index.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 
 /**
  * A container with information computed by an index - relations between
  * elements.
  */
 abstract class InternalIndexStore extends IndexStore {
   /**
@@ skipping 30 matching lines @@
   /**
    * Returns top-level [Element]s whose names satisfy to [nameFilter].
    */
   List<Element> getTopLevelDeclarations(ElementNameFilter nameFilter);
 
   /**
    * Records the declaration of the given top-level [element].
    */
   void recordTopLevelDeclaration(Element element);
 }