Make index provisional API.

pkg/analysis_server/lib/src/services/index/indexable_file.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 services.index.indexable_file;
 
-import 'package:analysis_server/plugin/index/index_core.dart';
+import 'package:analysis_server/src/provisional/index/index_core.dart';
 import 'package:analyzer/src/generated/engine.dart';
 
 /**
  * An [IndexableObject] which is used to index references to a file.
  */
 class IndexableFile implements IndexableObject {
   /**
    * The path of the file to be indexed.
    */
   @override
@@ skipping 47 matching lines @@
   IndexableFile decode(AnalysisContext context, String filePath, int offset) {
     return new IndexableFile(filePath);
   }
 
   @override
   int encodeHash(StringToInt stringToInt, IndexableFile indexable) {
     String path = indexable.path;
     return stringToInt(path);
   }
 }