Set send side bitrate estimate on successful probing attempt.

BUG=webrtc:5859

Review-Url: https://codereview.webrtc.org/2263973004
Cr-Commit-Position: refs/heads/master@{#13887}
diff --git a/webrtc/modules/bitrate_controller/include/bitrate_controller.h b/webrtc/modules/bitrate_controller/include/bitrate_controller.h
index f06314c..4c4578a 100644
--- a/webrtc/modules/bitrate_controller/include/bitrate_controller.h
+++ b/webrtc/modules/bitrate_controller/include/bitrate_controller.h
@@ -79,6 +79,8 @@
 
   virtual void UpdateDelayBasedEstimate(uint32_t bitrate_bps) = 0;
 
+  virtual void UpdateProbeBitrate(uint32_t bitrate_bps) = 0;
+
   // Gets the available payload bandwidth in bits per second. Note that
   // this bandwidth excludes packet headers.
   virtual bool AvailableBandwidth(uint32_t* bandwidth) const = 0;