Media Remoting: Draw remoting interstitial on poster image.

media/base/media_observer.h

Index: media/base/media_observer.h
diff --git a/media/base/media_observer.h b/media/base/media_observer.h
index 31357810f1c03ca5cb02e6fa104aa5b768820811..55558de179952a4e1b8326654285b5ffcc5c2d85 100644
--- a/media/base/media_observer.h
+++ b/media/base/media_observer.h
@@ -7,6 +7,7 @@
 
 #include "media/base/cdm_context.h"
 #include "media/base/pipeline_metadata.h"
+#include "url/gurl.h"
 
 namespace media {
 
@@ -40,6 +41,10 @@ class MEDIA_EXPORT MediaObserver {
   // Called when the media is playing/paused.
   virtual void OnPlaying() = 0;
   virtual void OnPaused() = 0;
+
+  // Called when a poster image URL is set, which happens when media is loaded
+  // or the poster attribute is changed.
+  virtual void OnSetPoster(const GURL& poster) = 0;
 };
 
 }  // namespace media