Update optimization guide histogram expiration date

Also changes dougarnett to mcrouse/sophiechang where appropriate

Bug: 1140005,1140000,1139999,1139998,1139997,1139996,1139995,1139994,1139993,1139992,1138428
Change-Id: Ie562d08a9038a7ff8fc4be093aa1f7771fa2cfc2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2485757
Commit-Queue: Sophie Chang <sophiechang@chromium.org>
Reviewed-by: Michael Crouse <mcrouse@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#819216}

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

@@ -10621,8 +10621,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Previews.OptOut.UserOptedOut" enum="PreviewsUserOptedOut"
-    expires_after="2020-01-31">
+    expires_after="2021-03-31">
   <owner>sophiechang@chromium.org</owner>
+  <owner>mcrouse@chromium.org</owner>
   <summary>
     Whether the user chose to reload the original page when shown a preview.
   </summary>