Add tracing AutoOpenCloseEvent.

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 <memory>
 #include <utility>
@@ skipping 816 matching lines @@
 
   if (!IsEnabled())
     return;
 
   if (dispatching_to_observer_list_) {
     DLOG(ERROR)
         << "Cannot manipulate TraceLog::Enabled state from an observer.";
     return;
   }
 
-  mode_ = DISABLED;
+  //mode_ = DISABLED;
 
   if (sampling_thread_) {
     // Stop the sampling thread.
     sampling_thread_->Stop();
     lock_.Release();
     PlatformThread::Join(sampling_thread_handle_);
     lock_.Acquire();
     sampling_thread_handle_ = PlatformThreadHandle();
     sampling_thread_.reset();
   }
@@ skipping 12 matching lines @@
       enabled_state_observer_list_;
   std::map<AsyncEnabledStateObserver*, RegisteredAsyncObserver> observer_map =
       async_observers_;
 
   {
     // Dispatch to observers outside the lock in case the observer triggers a
     // trace event.
     AutoUnlock unlock(lock_);
     for (EnabledStateObserver* observer : observer_list)
       observer->OnTraceLogDisabled();
+    mode_ = DISABLED;

[Primiano Tucci (use gerrit), 2016/09/14 09:38:54]

???

[alexandermont, 2016/09/14 20:14:57]

Reverted this change. Originally this was there because we were going to
effectively change OnTraceLogDisabled to be called before the trace log is
disabled; however it turned out that that made some unit tests fail. Now we're
going to change it to use OnBeforeTraceLogDisabled (unless we're going to change
it to something else...)

     for (const auto& it : observer_map) {
       it.second.task_runner->PostTask(
           FROM_HERE, Bind(&AsyncEnabledStateObserver::OnTraceLogDisabled,
                           it.second.observer));
     }
   }
   dispatching_to_observer_list_ = false;
 }
 
 int TraceLog::GetNumTracesRecorded() {
@@ skipping 1043 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