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
new file mode 100644
index 0000000000000000000000000000000000000000..77a5509cbb230d6c311a9c96f847e89a8adeb9fb
--- /dev/null
+++ b/sync/syncable/deferred_on_disk_directory_backing_store.h
@@ -0,0 +1,42 @@
+// 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 {
+
+// This is the concrete class that provides a useful implementation of
+// DirectoryBackingStore.
+class SYNC_EXPORT_PRIVATE DeferredOnDiskDirectoryBackingStore

[Nicolas Zea, 2014/08/11 18:12:25]

Does this need to be an implementation of DirectoryBackingStore? In general we
try to avoid this kind of inheritance in favor of composition. Or perhaps in
this case we can just have the OnDiskDirectoryBackingStore expose some logic to
control when it creates/destroys the directory?

[haitaol1, 2014/08/11 18:49:09]

I feel it's cleaner to use a separate class given the differences between normal
on-disk db and deferred on-disk db. The deferred on-disk db actually doesn't
depend on existing db file, so can be loaded in a simple way. It also requires
switching db on first save.

+    : 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_