[Picture-in-Picture] Add leavepictureinpicture video event

Bug: 806249
Change-Id: I443cedc0b6d0d72f98a61dd8bf5bb8c79da0d490
Reviewed-on: https://chromium-review.googlesource.com/895309
Reviewed-by: Mounir Lamouri (slow) <mlamouri@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: apacible <apacible@chromium.org>
Commit-Queue: Mounir Lamouri (slow) <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534388}
9 files changed