This will allow us to configure VP9 encoder to produce spatial layers with different frame rates. Bug: webrtc:9650 Change-Id: I3a9c58072003b8a8da681d5291d8f7ede7f52fa4 Reviewed-on: https://webrtc-review.googlesource.com/95427 Commit-Queue: Sergey Silkin <ssilkin@webrtc.org> Reviewed-by: Erik Språng <sprang@webrtc.org> Reviewed-by: Åsa Persson <asapersson@webrtc.org> Reviewed-by: Stefan Holmer <stefan@webrtc.org> Cr-Commit-Position: refs/heads/master@{#24435}