UMA stats for AudioRendererSinkCache utilization.

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 050453ff4e847a3950996a459419d85e35442550..9847609f8e9d32e23b5dbdbed38cf0ead0f80128 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -21327,6 +21327,31 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Media.Audio.SinkCache.GetOutputDeviceInfoHit"
+    enum="BooleanCacheHit">
+  <owner>olka@chromium.org</owner>
+  <summary>
+    Whether a cached sink was used to get audio output device information, or a
+    new one was created for that.
+  </summary>
+</histogram>
+
+<histogram name="Media.Audio.SinkCache.InfoSinkReusedForOutput"
+    enum="BooleanReused">
+  <owner>olka@chromium.org</owner>
+  <summary>
+    Whether a cached sink created to get audio output device information was

[Henrik Grunell, 2016/07/04 14:25:00]

This is hard to understand. I guess it explains my question in the other file,
but I'm still not sure.

[Henrik Grunell, 2016/07/04 14:40:59]

For example: "When audio output device information is requested, a sink is
created and queried for the information, then cached. This metric shows if such
a sink is later used for audio output, or cleared from the cache and deleted
without being used."

Actually, this is about sinks that were only used for getting device info in
their lifetime vs. sinks that were used for audio (and maybe device info). Maybe
word it and name the histogram something like that?

[o1ka, 2016/07/06 13:17:31]

Done.

+    reused for audio output or it was deleted unused after a timeout.
+  </summary>
+</histogram>
+
+<histogram name="Media.Audio.SinkCache.UsedForSinkCreation" enum="BooleanUsage">
+  <owner>olka@chromium.org</owner>
+  <summary>
+    Whether a sink was created through the sink cache or directly.
+  </summary>
+</histogram>
+
 <histogram name="Media.Audio.UptimeMac" units="hours">
   <owner>henrika@chromium.org</owner>
   <summary>