Add probe logging to RtcEventLog.

In this CL:
 - Add message BweProbeCluster and BweProbeResult to rtc_event_log.proto.
 - Add corresponding log functions to RtcEventLog.
 - Add optional field |probe_cluster_id| to RtpPacket message and added
   an overload function to log with this information.
 - Propagate the probe_cluster_id to where RTP packets are logged.

BUG=webrtc:6984

Review-Url: https://codereview.webrtc.org/2666533002
Cr-Commit-Position: refs/heads/master@{#16857}
diff --git a/webrtc/tools/event_log_visualizer/analyzer.cc b/webrtc/tools/event_log_visualizer/analyzer.cc
index 428c55c..564357c 100644
--- a/webrtc/tools/event_log_visualizer/analyzer.cc
+++ b/webrtc/tools/event_log_visualizer/analyzer.cc
@@ -457,6 +457,12 @@
         audio_network_adaptation_events_.push_back(ana_event);
         break;
       }
+      case ParsedRtcEventLog::BWE_PROBE_CLUSTER_CREATED_EVENT: {
+        break;
+      }
+      case ParsedRtcEventLog::BWE_PROBE_RESULT_EVENT: {
+        break;
+      }
       case ParsedRtcEventLog::UNKNOWN_EVENT: {
         break;
       }