[Extensions Metrics] Extend still-useful histograms

Extend Extensions.StartupPagesOverrides and
Extensions.SearchEngineOverrides by one year.

Bug: 1242490, 1244668
Change-Id: I3e22c1f07a9de24451c6ad0e6db95beba7a57852
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3141952
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Auto-Submit: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/main@{#918306}

tools/metrics/histograms/metadata/extensions/histograms.xml

@@ -3530,7 +3530,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Extensions.SearchEngineOverrides" units="units"
-    expires_after="2021-10-04">
+    expires_after="2022-10-04">
   <owner>rdevlin.cronin@chromium.org</owner>
   <owner>kelvinjiang@chromium.org</owner>
   <summary>
@@ -3645,7 +3645,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Extensions.StartupPagesOverrides" units="units"
-    expires_after="2021-10-10">
+    expires_after="2022-10-10">
   <owner>rdevlin.cronin@chromium.org</owner>
   <owner>kelvinjiang@chromium.org</owner>
   <summary>