Add probing to recover faster from large bitrate drops.

webrtc/modules/congestion_controller/send_side_congestion_controller.cc

Index: webrtc/modules/congestion_controller/send_side_congestion_controller.cc
diff --git a/webrtc/modules/congestion_controller/send_side_congestion_controller.cc b/webrtc/modules/congestion_controller/send_side_congestion_controller.cc
index 5328161e084896a89136f4d69e45bfd559158808..701fb7fdb70ea8bc5f9406f0a98c9e35a0a8ea0c 100644
--- a/webrtc/modules/congestion_controller/send_side_congestion_controller.cc
+++ b/webrtc/modules/congestion_controller/send_side_congestion_controller.cc
@@ -283,8 +283,10 @@ void SendSideCongestionController::OnTransportFeedback(
 
   bool currently_in_alr =
       pacer_->GetApplicationLimitedRegionStartTime().has_value();
-  if (!currently_in_alr && was_in_alr_) {
-    acknowledged_bitrate_estimator_->SetAlrEndedTimeMs(rtc::TimeMillis());
+  if (was_in_alr_ && !currently_in_alr) {
+    int64_t now_ms = rtc::TimeMillis();
+    acknowledged_bitrate_estimator_->SetAlrEndedTimeMs(now_ms);
+    probe_controller_->SetAlrEndedTimeMs(now_ms);
   }
   was_in_alr_ = currently_in_alr;
 
@@ -298,6 +300,9 @@ void SendSideCongestionController::OnTransportFeedback(
   }
   if (result.updated)
     bitrate_controller_->OnDelayBasedBweResult(result);
+  if (result.suggested_probe_bps) {
+    probe_controller_->RequestProbe(*result.suggested_probe_bps);
+  }
 }
 
 std::vector<PacketFeedback>