Trace loggging: Check for g_event_logger is not null before calling it.

webrtc/rtc_base/event_tracer.cc

 /*
  *  Copyright (c) 2012 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.
  */
 #include "webrtc/rtc_base/event_tracer.h"
@@ skipping 356 matching lines @@
 }  // namespace
 
 void SetupInternalTracer() {
   RTC_CHECK(rtc::AtomicOps::CompareAndSwapPtr(
                 &g_event_logger, static_cast<EventLogger*>(nullptr),
                 new EventLogger()) == nullptr);
   webrtc::SetupEventTracer(InternalGetCategoryEnabled, InternalAddTraceEvent);
 }
 
 void StartInternalCaptureToFile(FILE* file) {
-  g_event_logger->Start(file, false);
+  if (g_event_logger) {
+    g_event_logger->Start(file, false);
+  }
 }
 
 bool StartInternalCapture(const char* filename) {
+  if (!g_event_logger)
+    return false;
+
   FILE* file = fopen(filename, "w");
   if (!file) {
     LOG(LS_ERROR) << "Failed to open trace file '" << filename
                   << "' for writing.";
     return false;
   }
   g_event_logger->Start(file, true);
   return true;
 }
 
 void StopInternalCapture() {
-  g_event_logger->Stop();
+  if (g_event_logger) {
+    g_event_logger->Stop();
+  }
 }
 
 void ShutdownInternalTracer() {
   StopInternalCapture();
   EventLogger* old_logger = rtc::AtomicOps::AcquireLoadPtr(&g_event_logger);
   RTC_DCHECK(old_logger);
   RTC_CHECK(rtc::AtomicOps::CompareAndSwapPtr(
                 &g_event_logger, old_logger,
                 static_cast<EventLogger*>(nullptr)) == old_logger);
   delete old_logger;
   webrtc::SetupEventTracer(nullptr, nullptr);
 }
 
 }  // namespace tracing
 }  // namespace rtc