Add metrics for tracking underflow during src= playback.

I'm surprised we didn't already have these metrics, they are pretty
key to evaluating improvements to our pipeline. Possibly they were
harder to add prior to chcunningham@'s recent work to expose the
BUFFERING_HAVE_NOTHING state to WMPI.

BUG=641633
TEST=manual.

Review-Url: https://codereview.chromium.org/2286843003
Cr-Commit-Position: refs/heads/master@{#415215}

media/blink/webmediaplayer_impl.cc

@@ -226,7 +226,8 @@ WebMediaPlayerImpl::WebMediaPlayerImpl(
       overlay_surface_id_(SurfaceManager::kNoSurfaceID),
       suppress_destruction_errors_(false),
       can_suspend_state_(CanSuspendState::UNKNOWN),
-      is_encrypted_(false) {
+      is_encrypted_(false),
+      underflow_count_(0) {
   DCHECK(!adjust_allocated_memory_cb_.is_null());
   DCHECK(renderer_factory_);
   DCHECK(client_);
@@ -1099,6 +1100,14 @@ void WebMediaPlayerImpl::OnBufferingStateChange(BufferingState state) {
     // Once we have enough, start reporting the total memory usage. We'll also
     // report once playback starts.
     ReportMemoryUsage();
+
+    // Report the amount of time it took to leave the underflow state. Don't
+    // bother to report this for MSE playbacks since it's out of our control.
+    if (underflow_timer_ && data_source_) {
+      UMA_HISTOGRAM_TIMES("Media.UnderflowDuration",
+                          underflow_timer_->Elapsed());
+      underflow_timer_.reset();
+    }
   } else {
     // Buffering has underflowed.
     DCHECK_EQ(state, BUFFERING_HAVE_NOTHING);
@@ -1106,6 +1115,13 @@ void WebMediaPlayerImpl::OnBufferingStateChange(BufferingState state) {
     // HAVE_CURRENT_DATA.
     DCHECK_GT(highest_ready_state_, WebMediaPlayer::ReadyStateHaveCurrentData);
     SetReadyState(WebMediaPlayer::ReadyStateHaveCurrentData);
+
+    // Report the number of times we've entered the underflow state. Only report
+    // for src= playback since for MSE it's out of our control.
+    if (data_source_) {
+      UMA_HISTOGRAM_COUNTS_100("Media.UnderflowCount", ++underflow_count_);
+      underflow_timer_.reset(new base::ElapsedTimer());
+    }
   }
 
   UpdatePlayState();

media/blink/webmediaplayer_impl.h

@@ -18,6 +18,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/thread.h"
+#include "base/timer/elapsed_timer.h"
 #include "base/timer/timer.h"
 #include "build/build_config.h"
 #include "media/base/media_tracks.h"
@@ -541,6 +542,10 @@ class MEDIA_BLINK_EXPORT WebMediaPlayerImpl
   std::unique_ptr<WatchTimeReporter> watch_time_reporter_;
   bool is_encrypted_;
 
+  // Number of times we've reached BUFFERING_HAVE_NOTHING during playback.
+  int underflow_count_;
+  std::unique_ptr<base::ElapsedTimer> underflow_timer_;
+
   DISALLOW_COPY_AND_ASSIGN(WebMediaPlayerImpl);
 };
 

tools/metrics/histograms/histograms.xml

@@ -23471,6 +23471,20 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.UnderflowCount">
+  <owner>dalecurtis@chromium.org</owner>
+  <summary>
+    The number of times a src= playback has underflowed; i.e. ran out of data.
+  </summary>
+</histogram>
+
+<histogram name="Media.UnderflowDuration" units="ms">
+  <owner>dalecurtis@chromium.org</owner>
+  <summary>
+    The amount of time taken to leave the underflow state; i.e. resume playback.
+  </summary>
+</histogram>
+
 <histogram name="Media.URLScheme" enum="URLSchemeForHistogram">
   <owner>scherkus@chromium.org</owner>
   <summary>