When using the generic descriptor we want all simulcast streams to share one
frame id space (so that the SFU can switch stream without having to rewrite the
frame id). The state also needs to be restored when the RtpVideoSender is
recreated.
Note that |shared_simulcast_frame_id_| is only added, but not used in this CL.
Actually using it will be part of the next CL.
Bug: webrtc:9361
Change-Id: I7192a06d6ae4cab118ca5996ed99a56888ad1d97
Reviewed-on: https://webrtc-review.googlesource.com/92803
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24233}
