Extend dialog origin UMAs

Removing cross-origin dialogs is being worked on in
https://chromestatus.com/feature/5148698084376576. Make sure
that the relevant UMAs don't expire.

Fixed: 1130653
Bug: 1065085
Change-Id: I1fb2167f80e9b8337d4169f2236c84822dbce973
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2438891
Auto-Submit: Avi Drissman <avi@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Carlos IL <carlosil@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Carlos IL <carlosil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#811890}

tools/metrics/histograms/histograms_xml/others/histograms.xml

@@ -6757,9 +6757,10 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram base="true" name="JSDialogs.OriginRelationship"
-    enum="DialogOriginRelationship" expires_after="2020-11-01">
+    enum="DialogOriginRelationship" expires_after="2021-06-01">
   <owner>avi@chromium.org</owner>
   <owner>carlosil@chromium.org</owner>
+  <owner>ericmill@google.com</owner>
   <owner>meacer@chromium.org</owner>
   <summary>
     For dialogs, the relationship of the origins of the main frame vs the