[Passwords] Extend NumFormManagersCleared histogram

R=chromium-metrics-reviews@google.com

Fixed: 1140091
Change-Id: I91396a0be8deb6914e941b77f7aa2d7a32bdef52
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2490011
Commit-Queue: Mark Pearson <mpearson@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Auto-Submit: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823748}

tools/metrics/histograms/histograms_xml/password/histograms.xml

@@ -1569,8 +1569,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
-<histogram name="PasswordManager.NumFormManagersCleared" units="units"
-    expires_after="2020-11-29">
+<histogram name="PasswordManager.NumFormManagersCleared" units="count"
+    expires_after="M93">
   <owner>jdoerrie@chromium.org</owner>
   <owner>kazinova@google.com</owner>
   <summary>
@@ -1579,8 +1579,11 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
-<histogram name="PasswordManager.NumPasswordsNotShown" units="units"
-    expires_after="M90">
+<histogram name="PasswordManager.NumPasswordsNotShown" units="count"
+    expires_after="M79">
+  <obsolete>
+    Removed in M79.
+  </obsolete>
   <owner>jdoerrie@chromium.org</owner>
   <owner>vasilii@chromium.org</owner>
   <summary>