Some applications are having issues controlling how many active simulcast
layers they have and configuring them when the source track changes size
and rely on the old behavior automatically reducing the layer count.
Using the WebRTC-LegacySimulcastLayerLimit field trial, they can get back
the old behavior until they transition to the newer API.
Bug: webrtc:8785
Change-Id: I92d4dcd62b79a483a6a8867f97c5f502c6aa4db7
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/146709
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28666}