Add UMA stats for received frames or not in video track adapter.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 37715b1b9ff6ca1ab68983c68486a847492e288a..405350d029f975bd2f1d0f954d093399a3cae475 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -11441,6 +11441,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <summary>Metadata rotation in mp4 videos. Emitted during demuxing.</summary>
 </histogram>
 
+<histogram name="Media.VideoTrackAdapter.FramesReceived" enum="Boolean">

[Alexei Svitkine (slow), 2014/08/14 15:56:10]

Can you use a more specific enum? e.g. BooleanReceived (create it if it doesn't
exist yet)

[Henrik Grunell, 2014/08/14 21:23:32]

Done.

+  <owner>grunell@chromium.org</owner>
+  <owner>mcasas@chromium.org</owner>
+  <summary>If we received at least one frame during a session or not.</summary>

[Alexei Svitkine (slow), 2014/08/14 15:56:11]

Please clarify what "session" means, since that term can be overloaded. While
doing so, also mention when/how often this is recorded.

[Henrik Grunell, 2014/08/14 21:23:32]

Done.

+</histogram>
+
 <histogram name="Media.VideoVisibleAspectRatio">
   <owner>scherkus@chromium.org</owner>
   <summary>Visible aspect ratio of HTML5 video.</summary>