optional<int> initial_bitrate_interval_ms: time interval since start of call where fast adapt down is allowed. optional<double> initial_bitrate_factor: try fast adapt down if bw estimate is below initial bitrate * factor. Bug: none Change-Id: I63e1fdaac6556d8e9a961a42e11c925f9ecb9771 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/147725 Reviewed-by: Sergey Silkin <ssilkin@webrtc.org> Commit-Queue: Åsa Persson <asapersson@webrtc.org> Cr-Commit-Position: refs/heads/master@{#28753}