Extend Variations.Headers.* histograms.

Bug: 1144791
Change-Id: I3e66d25b9b92dc9662c29a6f5ea5a1ce21dc91bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2527890Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#827075}

tools/metrics/histograms/histograms_xml/variations/histograms.xml

@@ -121,7 +121,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Variations.Headers.DomainOwner" enum="VariationsHeadersOwner"
-    expires_after="2020-12-15">
+    expires_after="2021-11-08">
   <owner>caitlinfischer@google.com</owner>
   <owner>src/base/metrics/OWNERS</owner>
   <component>Internals&gt;Metrics</component>
@@ -147,7 +147,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Variations.Headers.RequestContextCategory"
-    enum="VariationsHeadersRequestContextCategory" expires_after="2020-12-15">
+    enum="VariationsHeadersRequestContextCategory" expires_after="2021-11-08">
   <owner>asvitkine@chromium.org</owner>
   <owner>jwd@chromium.org</owner>
   <owner>caitlinfischer@google.com</owner>