This makes Environment and thus field trials a required parameter, thus
RemoteBitrateEstimators member no longer need to fallback to the global field trial string.
Bug: webrtc:42220378
Change-Id: Ieb6ff442d5fde5fa9715573c758a7e078f0ceea4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/349922
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42314}
b84097e139