[Sync] Create new top-level sync/ directory

chrome/browser/sync/protocol/extension_setting_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 an extension setting.
-
-// Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
-// any fields in this file.
-
-syntax = "proto2";
-
-option optimize_for = LITE_RUNTIME;
-option retain_unknown_fields = true;
-
-package sync_pb;
-
-// Properties of extension setting sync objects.
-message ExtensionSettingSpecifics {
-  // Id of the extension the setting is for.
-  optional string extension_id = 1;
-
-  // Setting key.
-  optional string key = 2;
-
-  // Setting value serialized as JSON.
-  optional string value = 3;
-}
-