One feature that was missing from the new banner that was present in the

old was a confirmation dialog when discarding a draft review.

Additionally, we didn't have any kind of confirmation step when

discarding review request drafts. This change implements both of those

in the new UI.

Discarded review request drafts and review drafts. Saw the confirmation

dialog, which canceled the operation through either the escape key or

clicking the cancel button, and proceeded when clicking the discard

button.