[Sync] Move sync/{internal_api,syncable} into syncer namespace

sync/syncable/on_disk_directory_backing_store.h

 // 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.
 
 #ifndef SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_
 #define SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_
 #pragma once
 
 #include "base/file_path.h"
 #include "sync/syncable/directory_backing_store.h"
 
+namespace syncer {
 namespace syncable {
 
 // This is the concrete class that provides a useful implementation of
 // DirectoryBackingStore.
 class OnDiskDirectoryBackingStore : public DirectoryBackingStore {
  public:
   OnDiskDirectoryBackingStore(const std::string& dir_name,
                               const FilePath& backing_filepath);
   virtual DirOpenResult Load(
       MetahandlesIndex* entry_bucket,
       Directory::KernelLoadInfo* kernel_load_info) OVERRIDE;
 
  private:
   FilePath backing_filepath_;
 };
 
 }  // namespace syncable
+}  // namespace syncer
 
 #endif  // SYNC_SYNCABLE_ON_DISK_DIRECTORY_BACKING_STORE_H_