The code changes in this CL configure VP9 SVC to drop a superframe when the spatial base layer is dropped and to not drop upper spatial layers when the spatial base layer is not dropped. The changes are effective in non-flexible mode when codec_.mode == kRealtimeVideo and number of spatial layers > 1. Bug: none Change-Id: I27481b78f733cfc6c007d1ad9f45d69263853149 Reviewed-on: https://webrtc-review.googlesource.com/74261 Commit-Queue: Michael Horowitz <mhoro@webrtc.org> Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Reviewed-by: Rasmus Brandt <brandtr@webrtc.org> Cr-Commit-Position: refs/heads/master@{#23127}