[Media, Autoplay] Add UMA to record autoplay source

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 3b44d3b65a03ee68bf4486ffabeb43c0df0aff3b..e53f3ae07e3a91d9f6df29e4b6b2836477612212 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -20265,6 +20265,13 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.Audio.Autoplay" enum="AutoplaySource">
+  <owner>mlamouri@chromium.org</owner>
+  <owner>avayvod@chromium.org</owner>
+  <owner>zqzhang@chromium.org</owner>
+  <summary>Records the autoplay source of audios.</summary>
+</histogram>
+
 <histogram name="Media.Audio.Capture.FramesProvided" units="frames">
   <owner>grunell@chromium.org</owner>
   <summary>
@@ -21806,6 +21813,23 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.Video.Autoplay" enum="AutoplaySource">
+  <owner>mlamouri@chromium.org</owner>
+  <owner>avayvod@chromium.org</owner>
+  <owner>zqzhang@chromium.org</owner>
+  <summary>
+    Records the autoplay source of videos. This includes
+    Media.Video.Autoplay.Muted.
+  </summary>
+</histogram>
+
+<histogram name="Media.Video.Autoplay.Muted" enum="AutoplaySource">
+  <owner>mlamouri@chromium.org</owner>
+  <owner>avayvod@chromium.org</owner>
+  <owner>zqzhang@chromium.org</owner>
+  <summary>Records the autoplay source of muted videos.</summary>
+</histogram>
+
 <histogram name="Media.VideoCapture.AspectRatio" units="%">
   <owner>mcasas@chromium.org</owner>
   <summary>
@@ -63920,6 +63944,11 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="3" label="[Deprecated] AUTO_LAUNCH_FOREGROUND_USELESS"/>
 </enum>
 
+<enum name="AutoplaySource" type="int">
+  <int value="0" label="autoplay attribute"/>
+  <int value="1" label="play() method"/>
+</enum>
+
 <enum name="AutoSigninFirstRun" type="int">
   <int value="0" label="No action"/>
   <int value="1" label="Turn off"/>