[Media] Record time it takes to start rendering audio and video

media/renderers/renderer_impl.cc

Index: media/renderers/renderer_impl.cc
diff --git a/media/renderers/renderer_impl.cc b/media/renderers/renderer_impl.cc
index 87212d8214423f6ed38b7cd4344feca1ae16476e..9af325ee66461af57726b30d5a6d56c30bbbd68a 100644
--- a/media/renderers/renderer_impl.cc
+++ b/media/renderers/renderer_impl.cc
@@ -12,6 +12,7 @@
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/location.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/single_thread_task_runner.h"
 #include "base/strings/string_number_conversions.h"
 #include "media/base/audio_decoder_config.h"
@@ -215,10 +216,14 @@ void RendererImpl::StartPlayingFrom(base::TimeDelta time) {
 
   time_source_->SetMediaTime(time);
 
-  if (audio_renderer_)
+  if (audio_renderer_) {
+    audio_preroll_start_time_ = base::TimeTicks::Now();
     audio_renderer_->StartPlaying();
-  if (video_renderer_)
+  }
+  if (video_renderer_) {
+    video_preroll_start_time_ = base::TimeTicks::Now();
     video_renderer_->StartPlayingFrom(time);
+  }
 }
 
 void RendererImpl::RestartStreamPlayback(DemuxerStream* stream,
@@ -694,6 +699,18 @@ void RendererImpl::OnBufferingStateChange(DemuxerStream::Type type,
 
   // Renderer prerolled.
   if (was_waiting_for_enough_data && !WaitingForEnoughData()) {
+    if (type == DemuxerStream::AUDIO && !audio_preroll_start_time_.is_null()) {
+      UMA_HISTOGRAM_MEDIUM_TIMES(
+          "Media.Audio.PrerollTime",
+          base::TimeTicks::Now() - audio_preroll_start_time_);
+    } else if (type == DemuxerStream::VIDEO &&
+               !video_preroll_start_time_.is_null()) {
+      UMA_HISTOGRAM_MEDIUM_TIMES(
+          "Media.Video.PrerollTime",
+          base::TimeTicks::Now() - video_preroll_start_time_);
+      video_preroll_start_time_ = base::TimeTicks();
+    }
+
     StartPlayback();
     client_->OnBufferingStateChange(BUFFERING_HAVE_ENOUGH);
     return;