DCHECK that we don't insert nullptr into event log.

webrtc/logging/rtc_event_log/rtc_event_log.cc

Index: webrtc/logging/rtc_event_log/rtc_event_log.cc
diff --git a/webrtc/logging/rtc_event_log/rtc_event_log.cc b/webrtc/logging/rtc_event_log/rtc_event_log.cc
index ffeb9d2e4ad33ee20900a77297206ac34431a665..7d5b6062bffe4ea01adafd3727600c4688016d46 100644
--- a/webrtc/logging/rtc_event_log/rtc_event_log.cc
+++ b/webrtc/logging/rtc_event_log/rtc_event_log.cc
@@ -572,6 +572,8 @@ void RtcEventLogImpl::LogProbeResult(int id,
 }
 
 void RtcEventLogImpl::StoreEvent(std::unique_ptr<rtclog::Event>* event) {
+  RTC_DCHECK(event != nullptr);
+  RTC_DCHECK(event->get() != nullptr);
   if (!event_queue_.Insert(event)) {
     LOG(LS_ERROR) << "WebRTC event log queue full. Dropping event.";
   }