added uma stats to check the usage of media stream audio track audio processing

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 d51da5ae43595cf5e2fe16a8229ff3ae82f0f007..a3d186f5ab442bb92a0143170e46ddb1f1d433e9 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -7572,6 +7572,14 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="Media.AudioTrackProcessingStates"
+    enum="AudioTrackProcessingStates">
+  <summary>
+    State of the media stream audio track processing, sampled once during the
+    life time of a MediaStreamAudioProcessor.
+  </summary>
+</histogram>
+
 <histogram name="Media.CacheUseful" enum="BooleanSuccess">
   <owner>scherkus@chromium.org</owner>
   <summary>
@@ -26793,6 +26801,12 @@ other types of suffix sets.
   <int value="10" label="k192000Hz"/>
 </enum>
 
+<enum name="AudioTrackProcessingStates" type="int">
+  <int value="0" label="Enabled"/>
+  <int value="1" label="Disabled"/>
+  <int value="2" label="Processing in WebRTC"/>
+</enum>
+
 <enum name="AutocheckoutBubble" type="int">
   <obsolete>
     Deprecated as of 8/2013.