Gather UMA for click retarget due to DOM changes

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 441ddd975759eec65eb5b4aac562b77333853c84..33afb77a8e0ca4adfccd8a339f34c50177ceea9c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -15792,6 +15792,14 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Event.ClickNotFiredDueToDomManipulation">

[rkaplow, 2017/05/24 17:26:13]

can you add the enum (Boolean)

[Navid Zolghadr, 2017/05/24 20:49:48]

Done.

+  <owner>nzolghadr@chromium.org</owner>
+  <summary>
+    Number of times click target would be affected by DOM manipulation.   Team:

[rkaplow, 2017/05/24 17:26:13]

This isn't really the "number of times" since you're measuring a boolean. I
would describe this as if it was one event.

[Navid Zolghadr, 2017/05/24 20:49:48]

Done.

+    input-dev@chromium.org.
+  </summary>
+</histogram>
+
 <histogram name="Event.CoalescedCount.Mouse">
   <owner>tdresser@chromium.org</owner>
   Team: input-dev@chromium.org.