Added UMA metrics for MediaSourcePlayer and MediaCodecPlayer

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 c7a6b843898f0197b5982f07a03c6fc62acfc264..574d69415a43932f8964ef259d230249d38e7ac6 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -17677,6 +17677,30 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.MSE.Duration" units="seconds">
+  <owner>qinmin@chromium.org</owner>
+  <owner>timav@chromium.org</owner>
+  <summary>Duration of an uninterrupted MSE playback in seconds.</summary>

[xhwang, 2015/09/30 21:02:57]

+wolenetz as Media.MSE.Duration could be a general histogram not limited to
Clank. Matt: How is duration defined for MSE in general?

What's the exact meaning of "uninterrupted MSE playback"? What if the user seeks
during playback? Is this in wall clock time, or in media time?

In media, "Duration" has a clean meaning [1]. The "Media.Duration" UMA follows
this meaning. Here it seems we are recording something different. Can we use a
different name to avoid confusion? e.g. *.PlaybackDuration.

[1]
http://www.w3.org/html/wg/drafts/html/master/semantics.html#dom-media-duration

[Tima Vaisburd, 2015/10/01 20:05:15]

Added more explanation. This is the interval between playback actually starts
till pause, seek, release, etc. in media seconds.

+</histogram>
+
+<histogram name="Media.MSE.LateAudioFrames">

[qinmin, 2015/09/29 23:47:44]

I think LateAudioFramesPerMillion is better

[Ilya Sherman, 2015/09/30 04:20:03]

nit; You might also add units="frames per million" or something.

[Tima Vaisburd, 2015/09/30 18:50:10]

Added units but did not changes the histogram names, is this sufficient?

+  <owner>qinmin@chromium.org</owner>
+  <owner>timav@chromium.org</owner>
+  <summary>
+    Relative number of late audio frames wrt total number of audio frames in MSE

[xhwang, 2015/09/30 21:02:57]

Could you please elaborate what is exactly a "late audio frame"?

[Tima Vaisburd, 2015/10/01 20:05:15]

Added an explanation, this is related to potential underruns.

+    playback, multiplied by one million.
+  </summary>
+</histogram>
+
+<histogram name="Media.MSE.LateVideoFrames">

[qinmin, 2015/09/29 23:47:44]

ditto

+  <owner>qinmin@chromium.org</owner>
+  <owner>timav@chromium.org</owner>
+  <summary>
+    Relative number of late video frames wrt total number of video frames in MSE

[xhwang, 2015/09/30 21:02:57]

ditto

[Tima Vaisburd, 2015/10/01 20:05:15]

Added an explanation here as well.

+    playback, multiplied by one million.
+  </summary>
+</histogram>
+
 <histogram name="Media.MSE.NumberOfTracks">
   <owner>acolwell@chromium.org</owner>
   <summary>
@@ -17696,6 +17720,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.MSE.Starvations">
+  <owner>qinmin@chromium.org</owner>
+  <owner>timav@chromium.org</owner>
+  <summary>
+    Relative number of starvations wrt total number of frames in MSE playback,

[xhwang, 2015/09/30 21:02:57]

ditto, define "starvation".

[Tima Vaisburd, 2015/10/01 20:05:15]

Added here too.

+    multiplied by one million.
+  </summary>
+</histogram>
+
 <histogram name="Media.MSE.VideoCodec" enum="MSECodec">
   <owner>acolwell@chromium.org</owner>
   <summary>