Add confirmation when discarding a review request.
Review Request #5659 — Created March 28, 2014 and submitted
This prompts the user for confirmation when discarding a review request through
Close -> Discarded, which will help prevent accidental discards.
On a review request, I clicked Close -> Discarded, and got the confirmation
dialog. Clicking "Cancel" left the review request unchanged, and clicking "OK"
discarded the review request.