CC'ing some people that might be interested.

FWIW, I not 100% clear what information we could provide. I'w considering starting with only exposing a "playing fullscreen/dominant" API then maybe add something were it's possible to get status information about a dominant video.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e52c1b5442d81049d4b47b716d994ba746dde8a3

commit e52c1b5442d81049d4b47b716d994ba746dde8a3
Author: mlamouri <mlamouri@chromium.org>
Date: Thu Feb 23 14:57:50 2017

Provide a WebContents API to discover the playback of a fullscreen video.

That means a video is playing fullscreen, either directly (native controls) or
indirectly (custom controls). This is only exposed to the Java WebContents API
at the moment.

BUG= 690960 

Review-Url: https://codereview.chromium.org/2693203002
Cr-Commit-Position: refs/heads/master@{#452487}

[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/browser/media/media_web_contents_observer.cc
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/browser/media/media_web_contents_observer.h
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/browser/web_contents/web_contents_android.cc
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/browser/web_contents/web_contents_android.h
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/browser/web_contents/web_contents_impl.cc
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/browser/web_contents/web_contents_impl.h
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/common/media/media_player_delegate_messages.h
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/public/android/java/src/org/chromium/content/browser/webcontents/WebContentsImpl.java
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/public/android/java/src/org/chromium/content_public/browser/WebContents.java
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/renderer/media/renderer_webmediaplayer_delegate.cc
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/renderer/media/renderer_webmediaplayer_delegate.h
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/content/renderer/media/webmediaplayer_ms_unittest.cc
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/media/blink/webmediaplayer_delegate.h
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/media/blink/webmediaplayer_impl.cc
[modify] https://crrev.com/e52c1b5442d81049d4b47b716d994ba746dde8a3/media/blink/webmediaplayer_impl_unittest.cc