[Cast] VideoFrameFactory interface to vend frames with encoder affinity.

media/cast/sender/video_encoder_impl.cc

Index: media/cast/sender/video_encoder_impl.cc
diff --git a/media/cast/sender/video_encoder_impl.cc b/media/cast/sender/video_encoder_impl.cc
index a54ddfc7efdfc4bb0b9243dfbee047e59b9438a0..828eda46f96a1368cf69c18856f514a6d126b8b4 100644
--- a/media/cast/sender/video_encoder_impl.cc
+++ b/media/cast/sender/video_encoder_impl.cc
@@ -12,6 +12,7 @@
 #include "media/base/video_frame.h"
 #include "media/cast/cast_defines.h"
 #include "media/cast/sender/fake_software_video_encoder.h"
+#include "media/cast/sender/video_frame_factory.h"
 #include "media/cast/sender/vp8_encoder.h"
 
 namespace media {
@@ -121,5 +122,11 @@ void VideoEncoderImpl::LatestFrameIdToReference(uint32 frame_id) {
   dynamic_config_.latest_frame_id_to_reference = frame_id;
 }
 
+// Allow the encoder to return a specialized video frame factory. May return
+// null, in which case a default implementation will be used instead.
+scoped_refptr<VideoFrameFactory> VideoEncoderImpl::GetVideoFrameFactory() {
+  return nullptr;
+}
+
 }  //  namespace cast
 }  //  namespace media