Don't underflow for background rendering. Ensure accurate counts.

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 a5587443b1e35a02a729b2098acbc131adcff7c3..c035e5ea7136976a2ce7510d04e116daf3b17973 100644
--- a/media/blink/webmediaplayer_impl.cc
+++ b/media/blink/webmediaplayer_impl.cc
@@ -1136,17 +1136,20 @@ void WebMediaPlayerImpl::OnBufferingStateChange(BufferingState state) {
   } else {
     // Buffering has underflowed.
     DCHECK_EQ(state, BUFFERING_HAVE_NOTHING);
-    // It shouldn't be possible to underflow if we've not advanced past
-    // 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_) {
+    // for src= playback since for MSE it's out of our control. Ensure we only
+    // report the value when transitioning from HAVE_ENOUGH to HAVE_NOTHING.
+    if (data_source_ &&
+        ready_state_ == WebMediaPlayer::ReadyStateHaveEnoughData) {

[chcunningham, 2016/09/09 21:27:05]

I think this is fine, but I'm not sure it will have much impact. Looking at the
VideoRenderer guards, we only fire the event to transition to HAVE_NOTHING when
we are currently in HAVE_ENOUGH. Just want to be sure I'm not missing something.

[DaleCurtis, 2016/09/09 21:51:41]

Correct, that was my interpretation, but I wasn't able to verify it 100%.

       UMA_HISTOGRAM_COUNTS_100("Media.UnderflowCount", ++underflow_count_);
       underflow_timer_.reset(new base::ElapsedTimer());
     }
+
+    // It shouldn't be possible to underflow if we've not advanced past
+    // HAVE_CURRENT_DATA.
+    DCHECK_GT(highest_ready_state_, WebMediaPlayer::ReadyStateHaveCurrentData);
+    SetReadyState(WebMediaPlayer::ReadyStateHaveCurrentData);
   }
 
   UpdatePlayState();