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

sync/syncable/deferred_on_disk_directory_backing_store.h

Index: sync/syncable/deferred_on_disk_directory_backing_store.h
diff --git a/sync/syncable/deferred_on_disk_directory_backing_store.h b/sync/syncable/deferred_on_disk_directory_backing_store.h
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index 0000000000000000000000000000000000000000..9e6429a544a6def5707a22a18ae931cbf1c44e23
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+++ b/sync/syncable/deferred_on_disk_directory_backing_store.h
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+// 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_