Extending the expiry for Translate.TranslateTabIntentResult.

We will be running experiments using this starting in M88, but I
anticipate further integrations with Assistant will keep this metric
relevant at least until mid-year 2021. Setting this to M91 for now.

Bug: 1153777
Change-Id: I4fd788c6bed0220781ee1c6f519eab83a52e97bd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2572171Reviewed-by: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Josh Simmons <jds@google.com>
Cr-Commit-Position: refs/heads/master@{#833567}

tools/metrics/histograms/histograms_xml/translate/histograms.xml

@@ -911,12 +911,14 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Translate.TranslateTabIntentResult"
-    enum="TranslateTabIntentResult" expires_after="M89">
+    enum="TranslateTabIntentResult" expires_after="M91">
   <owner>jds@chromium.org</owner>
   <owner>chrome-language@google.com</owner>
   <summary>
     Android: Records the result of processing a TRANSLATE_TAB intent. See
     TranslateTabIntentResult in enums.xml for possible values.
+
+    This is recorded once for each TRANSLATE_TAB intent received.
   </summary>
 </histogram>