Flag which files I already reviewed on a Pull Request

When I do Code Review mostly on large Pull Requests (containing many files), and I have to stop it for some time and come back later to resume the Code Review, sometimes I do not remember which files I already reviewed.
This adds extra time on my Code Review process, since I would have to review some files again.
I would like to have a feature on the Pull Request page where I could flag which files I already reviewed.
Also, on the list of files on the top, I would like see an icon indicating if I already reviewed that file or not.