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

content/browser/web_contents/web_contents_impl.cc

Index: content/browser/web_contents/web_contents_impl.cc
diff --git a/content/browser/web_contents/web_contents_impl.cc b/content/browser/web_contents/web_contents_impl.cc
index 2daf76a0a060f226895085cd7feedadfe38e5cd6..08ef8e497e7998eace5d0872f9a2d60441130011 100644
--- a/content/browser/web_contents/web_contents_impl.cc
+++ b/content/browser/web_contents/web_contents_impl.cc
@@ -4256,6 +4256,10 @@ bool WebContentsImpl::HasPersistentVideo() const {
   return has_persistent_video_;
 }
 
+bool WebContentsImpl::HasActiveEffectivelyFullscreenVideo() const {
+  return media_web_contents_observer_->HasActiveEffectivelyFullscreenVideo();

[Charlie Reis, 2017/02/23 00:18:08]

I found this pretty weird at first glance-- that WebContents would implement a
method by asking one of its observers.  (Seems oddly circular.)

I think I understand now that MediaWebContentsObserver is really more of its own
class that manages some state (and happens to be a WebContentsObserver to get
its job done).  In that sense, maybe that class would make more sense if it
didn't have WebContentsObserver in its name?

Anyway, it's not a problem for this CL, and not something I feel too strongly
about.  Just a way to possibly reduce confusion in the future.

[mlamouri (slow - plz ping), 2017/02/23 13:34:19]

Ack

+}
+
 bool WebContentsImpl::IsFocusedElementEditable() {
   RenderFrameHostImpl* frame = GetFocusedFrame();
   return frame && frame->has_focused_editable_element();