[Picture-in-Picture] Detect if feature is enabled on Android.

This CL exposes a new internal setting that determines whether
Picture-in-Picture is enabled and if the user has disabled
Picture-in-Picture for Chrome using the system's per-application
settings. This setting is used in document.pictureInPictureEnabled and
video.requestPictureInPicture().

Test page: https://beaufortfrancois.github.io/sandbox/media/picture-in-picture-enabled
Screenshots: https://i.imgur.com/nLL3l0U.png
Recording: https://drive.google.com/file/d/1DgIH8XPPGr7giPvaFQ8bvDd_WM-1lzSj/view

Bug: 806249
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation;master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I6a4a8ca69c8b53a4bce3d8375c16725b3e545d52
Reviewed-on: https://chromium-review.googlesource.com/922081
Reviewed-by: Maria Khomenko <mariakhomenko@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Commit-Queue: François Beaufort <beaufort.francois@gmail.com>
Cr-Commit-Position: refs/heads/master@{#539085}
21 files changed