Extend the UKM purge sync metric.

Is still useful before unity has finished rolling out. Even post-unity we will want it (although it's now badly named).


Bug: 948338
Change-Id: I0cd3d2446d95049294d77e357d9838eb17d2079e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1594117
Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656796}
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 0b8cd3c..d65224d 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -130833,7 +130833,7 @@
 </histogram>
 
 <histogram name="UKM.SyncDisable.Purge" enum="Boolean"
-    expires_after="2019-05-01">
+    expires_after="2020-05-01">
   <owner>bcwhite@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <summary>