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 c3e29a1789f173d2cc62ad12845392cfaf1a70f7..4d061f6d3999d4af7aa8f7f9a48fdb3095865954 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 {
 
@@ -26,6 +27,10 @@ class MEDIA_EXPORT MediaObserver {
 
   // Called after demuxer is initialized.
   virtual void OnMetadataChanged(const PipelineMetadata& metadata) = 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