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}