tracing: Fix AddMetadataEvent race in presence of Convertable arguments

base/trace_event/trace_log.cc

 // Copyright 2015 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/trace_event/trace_log.h"
 
 #include <algorithm>
 #include <cmath>
 #include <utility>
 
@@ skipping 1332 matching lines @@
 
 void TraceLog::AddMetadataEvent(
     const char* name,
     int num_args,
     const char** arg_names,
     const unsigned char* arg_types,
     const unsigned long long* arg_values,
     const scoped_refptr<ConvertableToTraceFormat>* convertable_values,
     unsigned int flags) {
   scoped_ptr<TraceEvent> trace_event(new TraceEvent);
+  AutoLock lock(lock_);
   trace_event->Initialize(
       0,  // thread_id
       TimeTicks(), ThreadTicks(), TRACE_EVENT_PHASE_METADATA,
       &g_category_group_enabled[g_category_metadata], name,
       trace_event_internal::kNoId,  // id
       trace_event_internal::kNoId,  // bind_id
       num_args, arg_names, arg_types, arg_values, convertable_values, flags);
-  AutoLock lock(lock_);
   metadata_events_.push_back(std::move(trace_event));
 }
 
 // May be called when a COMPELETE event ends and the unfinished event has been
 // recycled (phase == TRACE_EVENT_PHASE_END and trace_event == NULL).
 std::string TraceLog::EventToConsoleMessage(unsigned char phase,
                                             const TimeTicks& timestamp,
                                             TraceEvent* trace_event) {
   AutoLock thread_info_lock(thread_info_lock_);
 
@@ skipping 367 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