Autoplay experiment metric fixes and additions.

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 bf75c1da4d3e2f98721452037320a82fc75f8899..88038c07782fb98ce40f9c2340655027ee642d0b 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -72865,6 +72865,14 @@ To add a new entry, add it with any value and run test to compute valid value.
   <int value="11" label="Any playback started."/>
   <int value="12" label="Any playback paused."/>
   <int value="13" label="Any playback bailed out."/>
+  <int value="14" label="Any playback completed."/>
+  <int value="15" label="Any audio element encountered."/>
+  <int value="16" label="Any video element encountered."/>
+  <int value="17" label="Autoplayed media complete."/>
+  <int value="18" label="Gestureless playback started due to load()."/>
+  <int value="19" label="Gesture requirement overridden for media stream."/>
+  <int value="20" label="Gesture requirement overridden, unknown reason."/>
+  <int value="21" label="Gesture requirement overridden by play method."/>
 </enum>
 
 <enum name="MediaGalleriesUsageType" type="int">