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

media/cast/sender/external_video_encoder.cc

Index: media/cast/sender/external_video_encoder.cc
diff --git a/media/cast/sender/external_video_encoder.cc b/media/cast/sender/external_video_encoder.cc
index 6dec102436ed50892f671ca1c5a33ca625e8603c..66a4790b770150057d167b026113ac3f025cb018 100644
--- a/media/cast/sender/external_video_encoder.cc
+++ b/media/cast/sender/external_video_encoder.cc
@@ -15,6 +15,7 @@
 #include "media/cast/cast_defines.h"
 #include "media/cast/logging/logging_defines.h"
 #include "media/cast/net/cast_transport_config.h"
+#include "media/cast/sender/video_frame_factory.h"
 #include "media/video/video_encode_accelerator.h"
 
 namespace media {
@@ -486,5 +487,13 @@ void ExternalVideoEncoder::GenerateKeyFrame() {
 void ExternalVideoEncoder::LatestFrameIdToReference(uint32 /*frame_id*/) {
   // Do nothing not supported.
 }
+
+// Creates a |VideoFrameFactory| object to vend |VideoFrame| object with
+// encoder affinity (defined as offering some sort of performance benefit). If
+// the encoder does not have any such capability, returns null.
+scoped_ptr<VideoFrameFactory> ExternalVideoEncoder::CreateVideoFrameFactory() {
+  return nullptr;
+}
+
 }  //  namespace cast
 }  //  namespace media