Extend the expiry of the App Banner histograms.

BUG=1151969

Change-Id: Ic9f451aee91e8473104996ca4194510577e0524f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2632106
Auto-Submit: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#845021}

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

@@ -531,7 +531,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="AppBanners.BeforeInstallEvent"
-    enum="AppBannersBeforeInstallEvent" expires_after="2021-01-01">
+    enum="AppBannersBeforeInstallEvent" expires_after="2021-06-01">
   <owner>dominickn@chromium.org</owner>
   <owner>pjmclachlan@google.com</owner>
   <summary>
@@ -594,7 +594,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="AppBanners.MinutesFromFirstVisitToBannerShown" units="minutes"
-    expires_after="2021-01-01">
+    expires_after="2021-06-01">
   <owner>dominickn@chromium.org</owner>
   <owner>pjmclachlan@google.com</owner>
   <summary>