* Stop encoding spatial layers S(n >= N) if application deactivates spatial layer N by setting RTCRtpEncodingParameters.active = false. * Move calculation of padding bitrate to SvcRateAllocator class. * Pad up to minimum required bitrate of base layer if ALR probing is enabled. Bug: webrtc:9350 Change-Id: I398284c943d43348def535c83263fc234c9767fa Reviewed-on: https://webrtc-review.googlesource.com/c/113240 Reviewed-by: Erik Språng <sprang@webrtc.org> Reviewed-by: Stefan Holmer <stefan@webrtc.org> Commit-Queue: Sergey Silkin <ssilkin@webrtc.org> Cr-Commit-Position: refs/heads/master@{#25945}