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}

webrtc/modules/bitrate_controller/bitrate_controller_impl.h

@@ -61,6 +61,8 @@ class BitrateControllerImpl : public BitrateController {
                             uint8_t* fraction_loss,
                             int64_t* rtt) override;
 
+  void UpdateProbeBitrate(uint32_t bitrate_bps) override;
+
   int64_t TimeUntilNextProcess() override;
   void Process() override;