[Structured metrics] Extend histogram expiry

We'll use the structured metrics  histograms at least until the end of
2021, so I've extended all of them.

Bug: 1160752
Change-Id: Ibd28eba932e442aa08b890e5fc4a8c8b57bdf6fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2627197Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Tony Yeoman <tby@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844413}

tools/metrics/histograms/histograms_xml/uma/histograms.xml

@@ -507,7 +507,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="UMA.StructuredMetrics.EventRecordingState"
-    enum="StructuredMetricsEventRecordingState" expires_after="2021-06-06">
+    enum="StructuredMetricsEventRecordingState" expires_after="2021-12-01">
   <owner>tby@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <owner>asvitkine@chromium.org</owner>
@@ -519,7 +519,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="UMA.StructuredMetrics.InternalError"
-    enum="StructuredMetricsInternalError" expires_after="2021-02-01">
+    enum="StructuredMetricsInternalError" expires_after="2021-12-01">
   <owner>tby@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <owner>asvitkine@chromium.org</owner>
@@ -530,7 +530,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="UMA.StructuredMetrics.KeyValidationState"
-    enum="StructuredMetricsKeyValidationState" expires_after="2021-06-06">
+    enum="StructuredMetricsKeyValidationState" expires_after="2021-12-01">
   <owner>tby@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <owner>asvitkine@chromium.org</owner>
@@ -542,7 +542,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="UMA.StructuredMetrics.NumEventsInUpload" units="count"
-    expires_after="2021-06-06">
+    expires_after="2021-12-01">
   <owner>tby@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <owner>asvitkine@chromium.org</owner>
@@ -553,7 +553,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="UMA.StructuredMetrics.PrefReadError"
-    enum="PrefServiceReadError" expires_after="2021-06-06">
+    enum="PrefServiceReadError" expires_after="2021-12-01">
   <owner>tby@chromium.org</owner>
   <owner>rkaplow@chromium.org</owner>
   <owner>asvitkine@chromium.org</owner>