Enable PictureInPictureAPI feature on Desktop.

Picture-in-Picture API is now enabled by default on Chrome OS, Linux,
Mac, and Windows. Android will come later.

Intent to ship: https://groups.google.com/a/chromium.org/d/msg/blink-dev/ibVPbqBQapU/rUZIrPPLAQAJ

Bug: 806249
Change-Id: I32fb2b491406e5592e57f64a5483bebf887ebdc0
Reviewed-on: https://chromium-review.googlesource.com/1090728
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#569186}
6 files changed