[Sync] Create new top-level sync/ directory

sync/protocol/app_notification_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 app notifications.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 24 matching lines @@
 
   // Payload - these fields are visible to the user content is defined by the
   // app. The fields are described in:
   // chrome/browser/extensions/app_notification.h
   optional string title = 4;
   optional string body_text = 5;
   optional string link_url = 6;
   optional string link_text = 7;
 }