WebRequest: Extend expiry of some histograms.

Extend expiry of Extensions.NetworkDelay and Extensions.NetworkDelayPercentage.
These are used to monitor webRequest API performance.

BUG=1149464

Change-Id: I26f5e6ef460c4677fc8d0fc85890aedbfab4dc62
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2553697Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830193}

tools/metrics/histograms/histograms_xml/extensions/histograms.xml

@@ -2703,7 +2703,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
-<histogram name="Extensions.NetworkDelay" units="ms" expires_after="2020-12-31">
+<histogram name="Extensions.NetworkDelay" units="ms" expires_after="2021-11-20">
   <owner>battre@chromium.org</owner>
   <owner>karandeepb@chromium.org</owner>
   <owner>extensions-core@chromium.org</owner>
@@ -2711,7 +2711,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Extensions.NetworkDelayPercentage" units="%"
-    expires_after="2021-05-16">
+    expires_after="2021-11-20">
   <owner>battre@chromium.org</owner>
   <owner>karandeepb@chromium.org</owner>
   <owner>extensions-core@chromium.org</owner>