Update histogram expiry date

The histogram is still used.

Fixed: 1149534
Change-Id: I4da9757d4751ddc09ee798e1ce2439b461a2b9ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542985
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#828694}

tools/metrics/histograms/histograms_xml/ios/histograms.xml

@@ -833,7 +833,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="IOS.Web.URLDidChangeToEmptyURL" enum="BooleanHit"
-    expires_after="2020-12-30">
+    expires_after="2021-11-30">
   <owner>gambard@chromium.org</owner>
   <owner>justincohen@chromium.org</owner>
   <summary>