add stylus metrics

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 a565afa1878b416164a64ea20d2c339073a75fe3..6eca8e20c845044833561d341fb16148c365a8ba 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -12714,6 +12714,20 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Event.DownEventCount.PerFormFactor" enum="DownEventFormFactor">
+  <owner>xiaoyinh@chromium.org</owner>
+  <summary>
+    Counts the number of down events generated by clamshell/touchview.
+  </summary>
+</histogram>
+
+<histogram name="Event.DownEventCount.PerInput" enum="DownEventSource">
+  <owner>xiaoyinh@chromium.org</owner>
+  <summary>
+    Counts the number of down events generated by Mouse/Touch/Stylus.
+  </summary>
+</histogram>
+
 <histogram name="Event.DragDrop.Cancel" enum="DragDropEventSource">
   <owner>mfomitchev@chromium.org</owner>
   <summary>
@@ -73827,6 +73841,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="2" label="GET_NON_CACHABLE"/>
 </enum>
 
+<enum name="DownEventFormFactor" type="int">
+  <int value="0" label="Clamshell"/>
+  <int value="1" label="Touchview"/>
+</enum>
+
+<enum name="DownEventSource" type="int">
+  <int value="0" label="Mouse"/>
+  <int value="1" label="Touch"/>
+  <int value="2" label="stylus"/>
+</enum>
+
 <enum name="DownloadContentDisposition" type="int">
   <int value="0" label="Content-Disposition header present"/>
   <int value="1" label="Valid"/>