To force SvcRateAllocator use propagated rather than global field trials Bug: webrtc:42220378 Change-Id: I0ca3186ee2428aafe3d7f093603b708e03ada121 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/362722 Commit-Queue: Åsa Persson <asapersson@webrtc.org> Auto-Submit: Danil Chapovalov <danilchap@webrtc.org> Reviewed-by: Åsa Persson <asapersson@webrtc.org> Cr-Commit-Position: refs/heads/main@{#43123}