Log created probe clusters to RtcEventLog.

webrtc/modules/pacing/bitrate_prober.h

Index: webrtc/modules/pacing/bitrate_prober.h
diff --git a/webrtc/modules/pacing/bitrate_prober.h b/webrtc/modules/pacing/bitrate_prober.h
index 0690750bbd50f0ef90c8a3646d857150d1a8f51c..510b2bd568515f70fc3311e65588ae76c93a5c99 100644
--- a/webrtc/modules/pacing/bitrate_prober.h
+++ b/webrtc/modules/pacing/bitrate_prober.h
@@ -18,12 +18,14 @@
 #include "webrtc/typedefs.h"
 
 namespace webrtc {
+class RtcEventLog;
 
 // Note that this class isn't thread-safe by itself and therefore relies
 // on being protected by the caller.
 class BitrateProber {
  public:
   BitrateProber();
+  explicit BitrateProber(RtcEventLog* event_log);
 
   void SetEnabled(bool enable);
 
@@ -100,6 +102,7 @@ class BitrateProber {
   int64_t next_probe_time_ms_;
 
   int next_cluster_id_;
+  RtcEventLog* const event_log_;
 };
 
 }  // namespace webrtc