DNR: Extend expiry of histograms.

Extend expiry of the following histograms:

  - Extensions.DeclarativeNetRequest.ReadDynamicRulesJSONStatus
  - Extensions.DeclarativeNetRequest.UpdateDynamicRulesStatus
  - Extensions.DeclarativeNetRequest.RulesetReindexSuccessful

BUG=1149533, 1149532

Change-Id: Id8bb35c0ece810b5c8cadd9f57eb14559cdbebc9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2541669Reviewed-by: Weilun Shi <sweilun@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828188}

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

@@ -670,7 +670,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Extensions.DeclarativeNetRequest.ReadDynamicRulesJSONStatus"
-    enum="ReadDynamicRulesJSONStatus" expires_after="2020-12-30">
+    enum="ReadDynamicRulesJSONStatus" expires_after="2021-06-01">
   <owner>karandeepb@chromium.org</owner>
   <owner>rdevlin.cronin@chromium.org</owner>
   <summary>
@@ -754,7 +754,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Extensions.DeclarativeNetRequest.RulesetReindexSuccessful"
-    enum="BooleanSuccess" expires_after="2020-12-30">
+    enum="BooleanSuccess" expires_after="2021-06-01">
   <owner>karandeepb@chromium.org</owner>
   <owner>lazyboy@chromium.org</owner>
   <summary>
@@ -766,7 +766,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Extensions.DeclarativeNetRequest.UpdateDynamicRulesStatus"
-    enum="UpdateDynamicRulesStatus" expires_after="2020-12-30">
+    enum="UpdateDynamicRulesStatus" expires_after="2021-06-01">
   <owner>karandeepb@chromium.org</owner>
   <owner>rdevlin.cronin@chromium.org</owner>
   <summary>