Allow XHProf profiles to be drag-and-dropped to upload them

Summary: Ref T12297. This could be fancier, but should make pulling profiles off admin.phacility.com significantly more realistic.

Test Plan: Dragged and dropped some profiles to upload them, then reviewed them via web UI.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12297

Differential Revision: https://secure.phabricator.com/D17401