The lowest and highest resolution layers are also identified instead of assuming they are the first and last ones. Bug: webrtc:10069 Change-Id: If9c76d647415c5065b79dc71850709db6bf16f61 Reviewed-on: https://webrtc-review.googlesource.com/c/114429 Reviewed-by: Erik Språng <sprang@webrtc.org> Commit-Queue: Florent Castelli <orphis@webrtc.org> Cr-Commit-Position: refs/heads/master@{#26343}