Add UMA to report requests for key systems using RequestMediaKeyAccess

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 260e8f5bb8d4419771e17834a615033cc7e0c292..a17bf4f6a1cdd7ab6a5e3c4d26cd54914d8fb360 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -12472,6 +12472,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Media.EME.RequestMediaKeySystemAccess"
+    enum="RequestMediaKeySystemAccessStatus">
+  <owner>sandersd@chromium.org</owner>
+  <summary>
+    Key system support query status and result, as reported by
+    RequestMediaKeySystemAccess. Each value will be reported at most once per
+    renderer process.
+  </summary>
+</histogram>
+
 <histogram name="Media.EME.Unknown" enum="CdmPromiseResult">
   <owner>sandersd@chromium.org</owner>
   <summary>
@@ -55767,6 +55777,11 @@ To add a new entry, add it with any value and run test to compute valid value.
   </int>
 </enum>
 
+<enum name="RequestMediaKeySystemAccessStatus" type="int">
+  <int value="0" label="Requested"/>
+  <int value="1" label="Supported"/>
+</enum>
+
 <enum name="ResolutionCategory" type="int">
   <int value="0" label="RESOLVE_SUCCESS"/>
   <int value="1" label="RESOLVE_FAIL"/>
@@ -62723,6 +62738,14 @@ To add a new entry, add it with any value and run test to compute valid value.
   <affected-histogram name="Event.Latency.RendererImpl"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="RequestMediaKeySystemAccessKeySystems" separator=".">
+  <suffix name="ClearKey" label="Requests for the Clear Key key system."/>
+  <suffix name="Unknown"
+      label="Requests for an unknown or unsupported key system."/>
+  <suffix name="Widevine" label="Requests for the Widevine key system."/>
+  <affected-histogram name="Media.EME.RequestMediaKeySystemAccess"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="ResourcePrefetchPredictorNetworkTypePrefetch"
     separator=".">
   <suffix name="NotPrefetched"