Add UMA stats for silence AudioInputController.

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 94e3845d52afa8b8dc23ee7c5e6335a47f9649ae..a8ea85914309e0f4ff5aec40fd784d69921611f1 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -10551,6 +10551,12 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Media.AudioInputControllerSessionSilenceReport"
+    enum="AudioInputSilenceReport">
+  <owner>grunell@chromium.org</owner>
+  <summary>The silence report for an audio input device session.</summary>
+</histogram>
+
 <histogram name="Media.AudioInputDeviceManager" units="ms">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>Measures the time taken for AudioInputDeviceManager::</summary>
@@ -36736,6 +36742,13 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   <int value="8" label="k1920"/>
 </enum>
 
+<enum name="AudioInputSilenceReport" type="int">
+  <int value="0" label="No measurement"/>
+  <int value="1" label="No silence"/>

[tommi (sloooow) - chröme, 2014/08/13 18:28:04]

"Have audio", "Audio good", "Audio received", etc... "no silence" sounds like
cacophony or something to me for some reason :)

[Henrik Grunell, 2014/08/14 11:21:45]

Done.

+  <int value="2" label="Only silence"/>
+  <int value="3" label="Partial silence"/>
+</enum>
+
 <enum name="AudioRendererEvents" type="int">
   <int value="0" label="Initialized"/>
   <int value="1" label="Runtime error"/>