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

content/browser/web_contents/web_contents_impl.h

Index: content/browser/web_contents/web_contents_impl.h
diff --git a/content/browser/web_contents/web_contents_impl.h b/content/browser/web_contents/web_contents_impl.h
index b7b3e51020d2e64f84a40b9bcc4176c399a179ca..57434f36850efa8ad34ea967bb0c8434d663a635 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -786,6 +786,11 @@ class CONTENT_EXPORT WebContentsImpl
   // Called when the WebContents gains or loses a persistent video.
   void SetHasPersistentVideo(bool value);
 
+  // Whether the WebContents has an active fullscreen video or a dominant video
+  // while the WebContents is fullscreen.
+  // |IsFullscreen| must return |true| when this method is called.

[liberato (no reviews please), 2017/02/14 23:00:01]

why?

[mlamouri (slow - plz ping), 2017/02/17 16:36:24]

The DCHECK() is just because it would basically mean checking the things
multiple time. Instead of having the callers make the call and the method check
too, better to have a "contract" which requires that callers know what they are
doing. The current expectations is that this would only be called while
fullscreen. It could change though.

+  virtual bool HasActiveFullscreenDominantVideo() const;
+
 #if defined(OS_ANDROID)
   // Called by FindRequestManager when all of the find match rects are in.
   void NotifyFindMatchRectsReply(int version,