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

media/cast/sender/video_sender.cc

Index: media/cast/sender/video_sender.cc
diff --git a/media/cast/sender/video_sender.cc b/media/cast/sender/video_sender.cc
index 16b7159befe1fd001ceb676d9ba1596a1ca90d99..190e9648d52ad4a6ffd85772b4046c903c76f160 100644
--- a/media/cast/sender/video_sender.cc
+++ b/media/cast/sender/video_sender.cc
@@ -15,6 +15,7 @@
 #include "media/cast/net/cast_transport_config.h"
 #include "media/cast/sender/external_video_encoder.h"
 #include "media/cast/sender/video_encoder_impl.h"
+#include "media/cast/sender/video_frame_factory.h"
 
 namespace media {
 namespace cast {
@@ -193,6 +194,12 @@ void VideoSender::InsertRawVideoFrame(
   }
 }
 
+scoped_ptr<VideoFrameFactory> VideoSender::CreateVideoFrameFactory() {
+  DCHECK(cast_initialization_status_ == STATUS_VIDEO_INITIALIZED);
+  DCHECK(video_encoder_.get()) << "Invalid state";
+  return video_encoder_->CreateVideoFrameFactory();
+}
+
 int VideoSender::GetNumberOfFramesInEncoder() const {
   return frames_in_encoder_;
 }