Remove non-standard document.createEvent('WebKitAnimationEvent').

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 19f4b0c02e241c5abce4b81dbcd9f1e96b84acbf..90b9ba7ade76025b8cb23ad96dea0bc25f71bdd7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -94836,7 +94836,7 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1184" label="DocumentCreateEventWheelEvent"/>
   <int value="1185" label="DocumentCreateEventMediaKeyEvent"/>
   <int value="1186" label="DocumentCreateEventTrackEvent"/>
-  <int value="1187" label="DocumentCreateEventWebKitAnimationEvent"/>
+  <int value="1187" label="OBSOLETE_DocumentCreateEventWebKitAnimationEvent"/>

[foolip, 2017/04/17 08:59:20]

I've always left histograms.xml alone when removing things from UseCounter.h, 
but I see there are some OBSOLETE_ entries here that show up in the names used
for chromstatus.com as well.

Is there a bug for doing something like this with all removed counters? I think
we'd need some kind of presubmit hook to keep things in a good state over time.

[tkent, 2017/04/18 01:39:32]

AFAIK, there were no bugs.  I filed
https://bugs.chromium.org/p/chromium/issues/detail?id=712485 .

   <int value="1188" label="DocumentCreateEventMutationEvents"/>
   <int value="1189" label="DocumentCreateEventOrientationEvent"/>
   <int value="1190" label="DocumentCreateEventSVGEvents"/>