[signin] Bump OAuth2Login.MergeSession* histograms

The MergeSession flow will be deprecated soon, it's better to keep the
histograms, as they may help in checking that the deprecation is going
well.

Fixed: 1140090
Change-Id: Ife217655abd9026f4eeecaf5ef5b136f7739d8a0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595746
Auto-Submit: David Roger <droger@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839641}

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

@@ -10510,7 +10510,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="OAuth2Login.MergeSessionFailure" enum="GoogleServiceAuthError"
-    expires_after="2020-11-29">
+    expires_after="2021-11-29">
   <owner>droger@chromium.org</owner>
   <owner>msarda@chromium.org</owner>
   <owner>chrome-signin-team@google.com</owner>
@@ -10521,7 +10521,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="OAuth2Login.MergeSessionRetry" enum="GoogleServiceAuthError"
-    expires_after="2020-11-29">
+    expires_after="2021-11-29">
   <owner>droger@chromium.org</owner>
   <owner>msarda@chromium.org</owner>
   <owner>chrome-signin-team@google.com</owner>