Add UMA metrics for VideoCodec.MP4 and VideoCodec.WebM

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 d476b29069e83525241378e66c58b9d231e3693f..43c90598084dc05eb684bfdac68a42f056c4c1a2 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -27825,6 +27825,22 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.MSE.VideoCodec.MP4" enum="MSECodec">
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    Video codec used in Media Source Extensions playback if the media container
+    is MP4. Set when AddId() is called during playback.
+  </summary>
+</histogram>
+
+<histogram name="Media.MSE.VideoCodec.WebM" enum="MSECodec">
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    Video codec used in Media Source Extensions playback if the media container
+    is WebM. Set when AddId() is called during playback.
+  </summary>
+</histogram>
+
 <histogram name="Media.Netflix.AudioBitrate" units="kbps">
   <obsolete>
     Deprecated 04/2016 as doesn't have data nor owner.
@@ -28628,6 +28644,20 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Video codec used in HTML5 media.</summary>
 </histogram>
 
+<histogram name="Media.VideoCodec.MP4" enum="VideoCodec">
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    Video codec used in HTML5 media if the media container is MP4.
+  </summary>
+</histogram>
+
+<histogram name="Media.VideoCodec.WebM" enum="VideoCodec">
+  <owner>media-dev@chromium.org</owner>
+  <summary>
+    Video codec used in HTML5 media if the media container is WebM.
+  </summary>
+</histogram>
+
 <histogram name="Media.VideoCodecProfile" enum="VideoCodecProfile">
   <owner>scherkus@chromium.org</owner>
   <summary>Video codec profile used in HTML5 media.</summary>