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 bbd794ca924a4d5f13a55352c9ccb7f39d12d193..41092b899de8cd45afe7991b2e74e24480c88927 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -17696,6 +17696,32 @@ 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>
+</histogram>
+
+<histogram name="Media.MSE.LateAudioFrames"
+    units="late frames per million frames">
+  <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
+    playback, multiplied by one million.
+  </summary>
+</histogram>
+
+<histogram name="Media.MSE.LateVideoFrames"
+    units="late frames per million frames">
+  <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
+    playback, multiplied by one million.
+  </summary>
+</histogram>
+
 <histogram name="Media.MSE.NumberOfTracks">
   <owner>acolwell@chromium.org</owner>
   <summary>
@@ -17715,6 +17741,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.MSE.Starvations" units="starvations per million frames">
+  <owner>qinmin@chromium.org</owner>
+  <owner>timav@chromium.org</owner>
+  <summary>
+    Relative number of starvations wrt total number of frames in MSE playback,
+    multiplied by one million.
+  </summary>
+</histogram>
+
 <histogram name="Media.MSE.VideoCodec" enum="MSECodec">
   <owner>acolwell@chromium.org</owner>
   <summary>