Implement snapshotting for non-Drive non-local file systems.

chrome/browser/chromeos/file_manager/snapshot_manager.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 CHROME_BROWSER_CHROMEOS_FILE_MANAGER_SNAPSHOT_MANAGER_H_
+#define CHROME_BROWSER_CHROMEOS_FILE_MANAGER_SNAPSHOT_MANAGER_H_
+
+#include "base/callback_forward.h"
+#include "base/files/file_path.h"
+#include "base/memory/ref_counted.h"
+
+class Profile;
+
+namespace base {
+class SequencedTaskRunner;
+}  // namespace base
+
+namespace file_manager {
+
+// Utility class for creating a snapshot file copy of a file system file.
+// Contrary to the underlying implementation of fileapi's CreateSnapshotFile,
+// the taken snapshot file will not be removed immediately. The life time is
+// managed by this manager class.

[hashimoto, 2014/06/19 02:26:01]

Why should we create a copy of the snapshot instead of keeping the file ref with
this class?

[kinaba, 2014/06/19 04:41:56]

That sounds far more better! Rewrote in the suggested approach and verified it
works.

+class SnapshotManager {
+ public:
+  // The callback type for CreateManagedSnapshot.
+  typedef base::Callback<void(const base::FilePath&)> LocalPathCallback;
+
+  explicit SnapshotManager(Profile* profile);
+  ~SnapshotManager();
+
+  // Creates a snapshot file copy of a file system file |absolute_file_path| and
+  // returns back to |callback|. Returns empty path for failure.
+  void CreateManagedSnapshot(const base::FilePath& absolute_file_path,
+                             const LocalPathCallback& callback);
+
+ private:
+  Profile* profile_;
+  scoped_refptr<base::SequencedTaskRunner> task_runner_;
+  base::FilePath base_path_;
+  DISALLOW_COPY_AND_ASSIGN(SnapshotManager);
+};
+
+}  // namespace file_manager
+
+#endif  // CHROME_BROWSER_CHROMEOS_FILE_MANAGER_SNAPSHOT_MANAGER_H_