Make index provisional API.

pkg/analysis_server/lib/src/services/index/store/codec.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.src.index.store.codec;
 
 import 'dart:collection';
 
-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/engine.dart';
 
 /**
  * A helper that encodes/decodes [AnalysisContext]s from/to integers.
  */
 class ContextCodec {
   /**
    * A table mapping contexts to their unique indices.
    */
@@ skipping 151 matching lines @@
   int encode(String name) {
     int index = nameToIndex[name];
     if (index == null) {
       index = _indexToName.length;
       nameToIndex[name] = index;
       _indexToName.add(name);
     }
     return index;
   }
 }