When a LossNotification RTCP message is received, the sequence numbers it refers to must be converted to timestamps before passing the message down to the encoder. This CL gives VideoSendStreamImpl access to that information via VideoSendStreamImpl::rtp_video_sender_. TBR=sprang@webrtc.org Bug: webrtc:10501 Change-Id: If207f0b6d2fb344da35b525cc104e8ba5cc614ec Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/131323 Commit-Queue: Elad Alon <eladalon@webrtc.org> Reviewed-by: Niels Moller <nisse@webrtc.org> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Cr-Commit-Position: refs/heads/master@{#27489}