Simulcast with one active stream: Use pixels from single active stream if set (instead of input stream which could be larger) to avoid going below the min_pixel_per_frame limit when downgrading resolution. Bug: none Change-Id: I65acb12cc53e46f726ccb5bfab8ce08ff0c4cf78 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/208101 Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org> Commit-Queue: Åsa Persson <asapersson@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33309}