Enable sync for the settings from the Extension Settings API.

chrome/browser/sync/protocol/nigori_specifics.proto

 // Copyright (c) 2011 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 47 matching lines @@
   optional bool encrypt_typed_urls = 18;
   optional bool encrypt_extensions = 19;
   optional bool encrypt_sessions = 20;
   optional bool encrypt_apps = 21;
   optional bool encrypt_search_engines = 22;
   
   optional bool sync_tabs = 23;
   
   // If true, all current and future datatypes will be encrypted.
   optional bool encrypt_everything = 24;
+
+  optional bool encrypt_extension_settings = 25;
 }
 
 extend EntitySpecifics {
   optional NigoriSpecifics nigori = 47745;
 }