Extend Viewport-related histograms to M97

Specifically, DidScalePage was expiring and is extended until M97 as
this is likely to be useful related to some questions of Double-Tap zoom
and Desktop vs. Mobile optimized pages. The other histograms are related
and likely to be helpful in this context too so I extended them all to
the same milestone.

Bug: 1165202
Change-Id: I6425d9930371ec66d72b469544fae409cff4b77f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627756
Commit-Queue: David Bokan <bokan@chromium.org>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Cr-Commit-Position: refs/heads/master@{#843600}

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

@@ -17043,7 +17043,7 @@ regressions. -->
 </histogram>
 
 <histogram name="Viewport.DidScalePage" enum="BooleanDidScalePage"
-    expires_after="M90">
+    expires_after="M97">
   <owner>bokan@chromium.org</owner>
   <owner>input-dev@chromium.org</owner>
   <summary>
@@ -17055,7 +17055,7 @@ regressions. -->
 </histogram>
 
 <histogram name="Viewport.MaxPageScale" enum="PageScaleFactorRange"
-    expires_after="2021-06-20">
+    expires_after="M97">
   <owner>bokan@chromium.org</owner>
   <owner>input-dev@chromium.org</owner>
   <summary>
@@ -17069,11 +17069,12 @@ regressions. -->
 </histogram>
 
 <histogram name="Viewport.MetaTagType" enum="MetaTagTypeEnum"
-    expires_after="M95">
+    expires_after="M97">
   <owner>bokan@chromium.org</owner>
   <owner>input-dev@chromium.org</owner>
   <summary>
     The viewport meta tag type seen on each page load. Only recorded on Android.
+    Recorded when the page finishes loading.
   </summary>
 </histogram>