[Sync] Add history delete directive type

sync/protocol/nigori_specifics.proto

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // Sync protocol datatype extension for nigori keys.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 76 matching lines @@
   optional bool encrypt_extension_settings = 25;
   optional bool encrypt_app_notifications = 26;
   optional bool encrypt_app_settings = 27;
 
   // User device information. Contains information about each device that has a
   // sync-enabled Chrome browser connected to the user account.
   repeated DeviceInformation device_information = 28;
   
   // Enable syncing favicons as part of tab sync.
   optional bool sync_tab_favicons = 29;
+
+  optional bool encrypt_history_delete_directives = 30;
 }