In preparation for moving creation of encoders to VideoStreamEncoder;
then this field is needed for calling
VideoEncoderFactory::CreateVideoEncoder.
Bug: webrtc:8830
Change-Id: Ie107a93596e22a5e7b9a9147bd85a93cf84b15a3
Reviewed-on: https://webrtc-review.googlesource.com/70221
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22894}