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 524e9c03947469e6e8e3c5dc9350bb22b79dc6d8..f70a1bc09f557d7e6e7c46f7618b63b4f7849ea4 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -68768,6 +68768,14 @@ 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">