UMA stats for stylus usage

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 378701f806a60e4b7402dc4c195bf67970d6504c..774f432040688a9812cb5130670b084dc675dc87 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -12789,6 +12789,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Event.DownEventCount.PerDestination"
+    enum="DownEventDestination">
+  <owner>xiaoyinh@chromium.org</owner>
+  <summary>
+    The number of down events received per destination. Every down event that is
+    targeted to each destination will be counted, include thoes who doesn't have

[Mark P, 2016/09/16 22:51:06]

two typos and wrong verb tenses.
include thoes who doesn't
->
including those that don't

[xiaoyinh(OOO Sep 11-29), 2016/09/19 21:19:53]

Thanks! Done.

+    an effect. For example: Tapping on a disabled button inside the browser
+    frame will be treated as down events on browser window.
+  </summary>
+</histogram>
+
 <histogram name="Event.DownEventCount.PerFormFactor" enum="DownEventFormFactor">
   <owner>xiaoyinh@chromium.org</owner>
   <summary>
@@ -75543,6 +75554,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="2" label="GET_NON_CACHABLE"/>
 </enum>
 
+<enum name="DownEventDestination" type="int">
+  <int value="0" label="Others, everything except browser and apps"/>
+  <int value="1" label="Inside the browser frame"/>
+  <int value="2" label="Regular chrome app, except default note-taking app"/>
+  <int value="3" label="ARC++ app (android app on Chrome)"/>
+  <int value="4" label="Default note-taking app"/>
+</enum>
+
 <enum name="DownEventFormFactor" type="int">
   <int value="0" label="Clamshell"/>
   <int value="1" label="Touchview"/>