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

media/renderers/audio_renderer_impl.cc

Index: media/renderers/audio_renderer_impl.cc
diff --git a/media/renderers/audio_renderer_impl.cc b/media/renderers/audio_renderer_impl.cc
index 4899be0a4b98470bf59c19947695bf431bb11610..41aae18b179b0ccf3f07bbee9ec02f54a6bbdcbb 100644
--- a/media/renderers/audio_renderer_impl.cc
+++ b/media/renderers/audio_renderer_impl.cc
@@ -14,6 +14,7 @@
 #include "base/callback_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/power_monitor/power_monitor.h"
 #include "base/single_thread_task_runner.h"
 #include "base/time/default_tick_clock.h"
@@ -172,6 +173,7 @@ void AudioRendererImpl::SetMediaTime(base::TimeDelta time) {
   start_timestamp_ = time;
   ended_timestamp_ = kInfiniteDuration;
   last_render_time_ = stop_rendering_time_ = base::TimeTicks();
+  start_rendering_time_ = tick_clock_->NowTicks();
   first_packet_timestamp_ = kNoTimestamp;
   audio_clock_.reset(new AudioClock(time, audio_parameters_.sample_rate()));
 }
@@ -777,6 +779,13 @@ int AudioRendererImpl::Render(base::TimeDelta delay,
       stop_rendering_time_ = base::TimeTicks();
     }
 
+    if (!start_rendering_time_.is_null()) {
+      UMA_HISTOGRAM_MEDIUM_TIMES(
+          "Media.Audio.FirstRenderTime",
+          tick_clock_->NowTicks() - start_rendering_time_);
+      start_rendering_time_ = base::TimeTicks();
+    }
+
     // Ensure Stop() hasn't destroyed our |algorithm_| on the pipeline thread.
     if (!algorithm_) {
       audio_clock_->WroteAudio(0, frames_requested, frames_delayed,