Button to cycle through comments by a given user

Often I would like to go back to an older comment someone made, but it is difficult to find in the older comments, or sometimes the comment disappears entirely (I've seen this when the comment is on a commit message which gets modified). It would be useful to have a `reviewer` button, similar to the `unreviewed` or `unresolved` buttons, but with a drop-down arrow to select a specific user who has left comments. Subsequent clicks of that button would cycle through all of the comments left by that user.