[Picture-in-Picture] Add enterpictureinpicture video event

Bug: 806249
Change-Id: I64d5e3aeea52b04c4f79e5b7d302f6ffe914ff8a
Reviewed-on: https://chromium-review.googlesource.com/893461
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Mounir Lamouri (slow) <mlamouri@chromium.org>
Reviewed-by: apacible <apacible@chromium.org>
Commit-Queue: Mounir Lamouri (slow) <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534049}
9 files changed