Fix crash in TraceLog::UpdateTraceEventDuration()

base/debug/trace_event_impl.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/debug/trace_event_impl.h"
 
 #include <algorithm>
 
 #include "base/base_switches.h"
 #include "base/bind.h"
@@ skipping 1935 matching lines @@
 
     if (trace_options() & ECHO_TO_CONSOLE) {
       lock.EnsureAcquired();
       OutputEventToConsoleWhileLocked(TRACE_EVENT_PHASE_END, now, trace_event);
     }
   }
 
   if (*category_group_enabled & ENABLED_FOR_EVENT_CALLBACK) {
     EventCallback event_callback = reinterpret_cast<EventCallback>(
         subtle::NoBarrier_Load(&event_callback_));
-    event_callback(now, TRACE_EVENT_PHASE_END, category_group_enabled, name,
-                   trace_event_internal::kNoEventId, 0, NULL, NULL, NULL,
-                   TRACE_EVENT_FLAG_NONE);
+    if (event_callback) {
+      event_callback(now, TRACE_EVENT_PHASE_END, category_group_enabled, name,
+                     trace_event_internal::kNoEventId, 0, NULL, NULL, NULL,
+                     TRACE_EVENT_FLAG_NONE);
+    }
   }
 }
 
 void TraceLog::SetWatchEvent(const std::string& category_name,
                              const std::string& event_name) {
   const unsigned char* category = GetCategoryGroupEnabled(
       category_name.c_str());
   AutoLock lock(lock_);
   subtle::NoBarrier_Store(&watch_category_,
                           reinterpret_cast<subtle::AtomicWord>(category));
@@ skipping 343 matching lines @@
 }
 
 ScopedTraceBinaryEfficient::~ScopedTraceBinaryEfficient() {
   if (*category_group_enabled_) {
     TRACE_EVENT_API_UPDATE_TRACE_EVENT_DURATION(category_group_enabled_,
                                                 name_, event_handle_);
   }
 }
 
 }  // namespace trace_event_internal