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 813e35e1609baa118fafdf72d67af3deb7886fca..7c26aa8f3c72ec35a50b40d44995b50ab6bf0ee3 100644
--- a/content/browser/web_contents/web_contents_impl.h
+++ b/content/browser/web_contents/web_contents_impl.h
@@ -793,6 +793,13 @@ class CONTENT_EXPORT WebContentsImpl
   // Called when the WebContents gains or loses a persistent video.
   void SetHasPersistentVideo(bool value);
 
+  // Whether the WebContents has an active player is effectively fullscreen.
+  // That means that the video is either fullscreen or it is the content of
+  // a fullscreen page (in other words, a fullscreen video with custom
+  // controls).
+  // |IsFullscreen| must return |true| when this method is called.
+  bool HasActiveEffectivelyFullscreenVideo() const;
+
 #if defined(OS_ANDROID)
   // Called by FindRequestManager when all of the find match rects are in.
   void NotifyFindMatchRectsReply(int version,