GitLab

Use a ButtonHandler for the play/pause and close buttons so
they can be picked up by voiceover.

BUG=848509

Change-Id: I6fb063c03156d48b814fd3d370703724753a0b29
Reviewed-on: https://chromium-review.googlesource.com/1153623
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: apacible <apacible@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578821}