Include playbacks which never underflow in underflow metrics.

media/blink/webmediaplayer_impl.cc

Index: media/blink/webmediaplayer_impl.cc
diff --git a/media/blink/webmediaplayer_impl.cc b/media/blink/webmediaplayer_impl.cc
index cde7e38e0a693f2e56086525005bb4e2d23efc8e..1fdcda87de2b80b4d16b869dc862b741da5c1dd5 100644
--- a/media/blink/webmediaplayer_impl.cc
+++ b/media/blink/webmediaplayer_impl.cc
@@ -1084,6 +1084,15 @@ void WebMediaPlayerImpl::OnBufferingStateChange(BufferingState state) {
     return;
 
   if (state == BUFFERING_HAVE_ENOUGH) {
+    if (data_source_ &&
+        highest_ready_state_ < WebMediaPlayer::ReadyStateHaveEnoughData) {
+      DCHECK_EQ(underflow_count_, 0);
+      // Record a zero value for underflow histograms so that the histogram
+      // includes playbacks which never encounter an underflow event.
+      UMA_HISTOGRAM_COUNTS_100("Media.UnderflowCount", 0);

[Steven Holte, 2016/09/07 00:24:26]

You should probably consolidate the macro calls for these histograms into a
single location, using a helper function, since each call will create a local
static variable.

+      UMA_HISTOGRAM_TIMES("Media.UnderflowDuration", base::TimeDelta());
+    }
+
     // TODO(chcunningham): Monitor playback position vs buffered. Potentially
     // transition to HAVE_FUTURE_DATA here if not enough is buffered.
     SetReadyState(WebMediaPlayer::ReadyStateHaveEnoughData);