Revert of Let SyncBackupManager keep backup data in memory until shutdown. Only persist

sync/syncable/deferred_on_disk_directory_backing_store.h

-// Copyright 2014 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_DEFERRED_ON_DISK_DIRECTORY_BACKING_STORE_H_
-#define SYNC_SYNCABLE_DEFERRED_ON_DISK_DIRECTORY_BACKING_STORE_H_
-
-#include "base/files/file_path.h"
-#include "sync/base/sync_export.h"
-#include "sync/syncable/directory_backing_store.h"
-
-namespace syncer {
-namespace syncable {
-
-// Store used for backing up user's data before first sync. It creates an
-// in-memory store first and switch to on-disk store if SaveChanges() is
-// called, which only happens when SyncBackupManager is shut down and a
-// syncing backend is to be created. Thus we guarantee that user data is not
-// persisted until user is actually going to sync.
-class SYNC_EXPORT_PRIVATE DeferredOnDiskDirectoryBackingStore
-    : public DirectoryBackingStore {
- public:
-  DeferredOnDiskDirectoryBackingStore(const std::string& dir_name,
-                                      const base::FilePath& backing_filepath);
-  virtual ~DeferredOnDiskDirectoryBackingStore();
-  virtual DirOpenResult Load(
-      Directory::MetahandlesMap* handles_map,
-      JournalIndex* delete_journals,
-      Directory::KernelLoadInfo* kernel_load_info) OVERRIDE;
-  virtual bool SaveChanges(const Directory::SaveChangesSnapshot& snapshot)
-      OVERRIDE;
-
- private:
-  base::FilePath backing_filepath_;
-
-  // Whether current DB is on disk.
-  bool db_is_on_disk_;
-
-  DISALLOW_COPY_AND_ASSIGN(DeferredOnDiskDirectoryBackingStore);
-};
-
-}  // namespace syncable
-}  // namespace syncer
-
-#endif  // SYNC_SYNCABLE_DEFERRED_ON_DISK_DIRECTORY_BACKING_STORE_H_