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

content/renderer/media/renderer_webmediaplayer_delegate.cc

Index: content/renderer/media/renderer_webmediaplayer_delegate.cc
diff --git a/content/renderer/media/renderer_webmediaplayer_delegate.cc b/content/renderer/media/renderer_webmediaplayer_delegate.cc
index 92d1140e8a6c52c2500f4daa21383717f482f37d..633b5f77ab2565110d99db0bae538893ea5fb379 100644
--- a/content/renderer/media/renderer_webmediaplayer_delegate.cc
+++ b/content/renderer/media/renderer_webmediaplayer_delegate.cc
@@ -168,6 +168,12 @@ bool RendererWebMediaPlayerDelegate::IsStale(int player_id) {
   return stale_players_.count(player_id);
 }
 
+void RendererWebMediaPlayerDelegate::SetIsFullscreen(int player_id,
+                                                     bool is_fullscreen) {
+  Send(new MediaPlayerDelegateHostMsg_OnMediaFullscreenChange(
+      routing_id(), player_id, is_fullscreen));
+}
+
 void RendererWebMediaPlayerDelegate::WasHidden() {
   RecordAction(base::UserMetricsAction("Media.Hidden"));