Number of temporal layers in screen sharing was unintentionally changed from 3 to 2 in a796a7ee85b8805a92e21f888a893bef1581bfee. This changes the value to 3. Bug: webrtc:9013 Change-Id: I68291b49276afd2689f20d1c3581e149aa6fd610 Reviewed-on: https://webrtc-review.googlesource.com/61860 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@{#22621}