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

webrtc/logging/rtc_event_log/rtc_event_log.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 554 matching lines @@
 
   auto probe_result = event->mutable_probe_result();
   probe_result->set_id(id);
   probe_result->set_result(result);
   if (result == rtclog::BweProbeResult::SUCCESS)
     probe_result->set_bitrate_bps(bitrate_bps);
   StoreEvent(&event);
 }
 
 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.";
   }
   helper_thread_.SignalNewEvent();
 }
 
 bool RtcEventLog::ParseRtcEventLog(const std::string& file_name,
                                    rtclog::EventStream* result) {
   char tmp_buffer[1024];
   int bytes_read = 0;
@@ skipping 27 matching lines @@
 #else
   return std::unique_ptr<RtcEventLog>(new RtcEventLogNullImpl());
 #endif  // ENABLE_RTC_EVENT_LOG
 }
 
 std::unique_ptr<RtcEventLog> RtcEventLog::CreateNull() {
   return std::unique_ptr<RtcEventLog>(new RtcEventLogNullImpl());
 }
 
 }  // namespace webrtc