mac: Add profiling for MediaStreamManager::StartMonitoringOnUIThread.

content/browser/renderer_host/media/media_stream_manager.cc

Index: content/browser/renderer_host/media/media_stream_manager.cc
diff --git a/content/browser/renderer_host/media/media_stream_manager.cc b/content/browser/renderer_host/media/media_stream_manager.cc
index 11bfb0ed242c5cd9471ebf9f48f03cfcd175c374..cf9e36b06f3b840e484bdd40727d567e5b2ee9d8 100644
--- a/content/browser/renderer_host/media/media_stream_manager.cc
+++ b/content/browser/renderer_host/media/media_stream_manager.cc
@@ -12,6 +12,7 @@
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "base/power_monitor/power_monitor.h"
+#include "base/profiler/scoped_tracker.h"
 #include "base/rand_util.h"
 #include "base/run_loop.h"
 #include "base/strings/stringprintf.h"
@@ -965,6 +966,11 @@ void MediaStreamManager::StopRemovedDevice(const MediaStreamDevice& device) {
 }
 
 void MediaStreamManager::StartMonitoring() {
+  // TODO(erikchen): Remove ScopedTracker below once crbug.com/458404 is fixed.
+  tracked_objects::ScopedTracker tracking_profile1(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "458404 MediaStreamManager::StartMonitoring"));
+
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   if (monitoring_started_)
     return;
@@ -975,10 +981,19 @@ void MediaStreamManager::StartMonitoring() {
   monitoring_started_ = true;
   base::SystemMonitor::Get()->AddDevicesChangedObserver(this);
 
+  // TODO(erikchen): Remove ScopedTracker below once crbug.com/458404 is fixed.
+  tracked_objects::ScopedTracker tracking_profile2(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "458404 MediaStreamManager::StartMonitoring::EnumerateAudio"));
   // Enumerate both the audio and video devices to cache the device lists
   // and send them to media observer.
   ++active_enumeration_ref_count_[MEDIA_DEVICE_AUDIO_CAPTURE];
   audio_input_device_manager_->EnumerateDevices(MEDIA_DEVICE_AUDIO_CAPTURE);
+
+  // TODO(erikchen): Remove ScopedTracker below once crbug.com/458404 is fixed.
+  tracked_objects::ScopedTracker tracking_profile3(
+      FROM_HERE_WITH_EXPLICIT_FUNCTION(
+          "458404 MediaStreamManager::StartMonitoring::EnumerateVideo"));
   ++active_enumeration_ref_count_[MEDIA_DEVICE_VIDEO_CAPTURE];
   video_capture_manager_->EnumerateDevices(MEDIA_DEVICE_VIDEO_CAPTURE);