Add loss-based BWE experiment which allows us to try different parameters.

webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.h

Index: webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.h
diff --git a/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.h b/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.h
index a300ad1e90f0e39455011510138d0cbd966ea8d6..84ee882982bdd465ede7b9a3923cea8f6969e984 100644
--- a/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.h
+++ b/webrtc/modules/bitrate_controller/send_side_bandwidth_estimation.h
@@ -99,6 +99,9 @@ class SendSideBandwidthEstimation {
   RtcEventLog* event_log_;
   int64_t last_rtc_event_log_ms_;
   bool in_timeout_experiment_;
+  float low_loss_threshold_;
+  float high_loss_threshold_;
+  uint32_t bitrate_threshold_bps_;
 };
 }  // namespace webrtc
 #endif  // WEBRTC_MODULES_BITRATE_CONTROLLER_SEND_SIDE_BANDWIDTH_ESTIMATION_H_