Chrome OS: Mark Settings.PinUnlockSetup UMA histogram to expire after M97.

Bug: 975778
Change-Id: Idfba9b707ff815568553cb8d510b99f697764095
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1710864Reviewed-by: Jesse Doherty <jwd@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680266}

tools/metrics/histograms/histograms.xml

@@ -123665,8 +123665,9 @@ should be kept until we remove incident reporting. -->
 </histogram>
 
 <histogram name="Settings.PinUnlockSetup" enum="LockScreenProgress"
-    expires_after="M77">
-  <owner>sammiequon@chromium.org</owner>
+    expires_after="M97">
+  <owner>rsorokin@chromium.org</owner>
+  <owner>jessejames@chromium.org</owner>
   <summary>
     The users progress through the pin unlock setup wizard. Each type
     corresponds to the user completeing a different stage of the setup wizard.