[Sync] Create new top-level sync/ directory

sync/protocol/sync_enums.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 for communication between sync client and server.
 
 // Update proto_value_conversions{.h,.cc,_unittest.cc} if you change
 // any fields in this file.
 
 syntax = "proto2";
@@ skipping 44 matching lines @@
     MIGRATION_DONE     = 9;   // Migration has finished for one or more data
                               // types.  Client should clear the cache for
                               // these data types only and then re-sync with
                               // a server.
     UNKNOWN            = 100; // Unknown value. This should never be explicitly
                               // used; it is the default value when an
                               // out-of-date client parses a value it doesn't
                               // recognize.
   }
 }