[PaintHolding] Extend the PaintHolding.* UMA

We would still like to track these until Paint Holding Cross
Origin is well and truly launched.

Fixed: 1156203
Change-Id: Id85cb3cc280bf681161a877ed797ffa06ba43cdc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2622998
Auto-Submit: Stephen Chenney <schenney@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#842670}

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

@@ -11131,7 +11131,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="PaintHolding.CommitTrigger2" enum="PaintHoldingCommitTrigger2"
-    expires_after="2021-01-15">
+    expires_after="2021-07-15">
   <owner>schenney@chromium.org</owner>
   <owner>paint-dev@chromium.org</owner>
   <summary>
@@ -11141,7 +11141,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="PaintHolding.InputTiming2" enum="PaintHoldingInputTiming"
-    expires_after="2021-01-15">
+    expires_after="2021-07-15">
   <owner>schenney@chromium.org</owner>
   <owner>paint-dev@chromium.org</owner>
   <summary>