Update expiration for printing metrics

ChromeOS Printing is actively using:
Printing.CUPS.PrinterAdded
Printing.CUPS.PrinterRemoved
Printing.CUPS.PrintersDiscovered
Printing.CUPS.PrinterSetupResult

to monitor printer setup health.

Bug: 1089320
Change-Id: Iefa06c26161190f9c422b7dfafaaf7be1050892f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2451519
Commit-Queue: Sean Kau <skau@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814377}

tools/metrics/histograms/histograms_xml/printing/histograms.xml

@@ -223,8 +223,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Printing.CUPS.PrinterAdded" enum="PrinterProtocol"
-    expires_after="M85">
+    expires_after="2021-10-01">
   <owner>skau@chromium.org</owner>
+  <owner>src/chromeos/printing/OWNERS</owner>
   <summary>
     The protocol for a printer that was added. Used to track printer churn by
     protocol. Only on Chrome OS.
@@ -232,8 +233,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Printing.CUPS.PrinterRemoved" enum="PrinterProtocol"
-    expires_after="M85">
+    expires_after="2021-10-01">
   <owner>skau@chromium.org</owner>
+  <owner>src/chromeos/printing/OWNERS</owner>
   <summary>
     The protocol for a printer that was removed. Used to track printer churn by
     protocol. Only on Chrome OS.
@@ -241,8 +243,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Printing.CUPS.PrintersDiscovered" units="printers"
-    expires_after="M85">
+    expires_after="2021-10-01">
   <owner>skau@chromium.org</owner>
+  <owner>src/chromeos/printing/OWNERS</owner>
   <summary>
     The number of printers shown in the discovered printers dialog during
     printer set up. Only recorded on Chrome OS.
@@ -250,8 +253,9 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="Printing.CUPS.PrinterSetupResult" enum="PrinterSetupResult"
-    expires_after="M85">
+    expires_after="2021-10-01">
   <owner>skau@chromium.org</owner>
+  <owner>src/chromeos/printing/OWNERS</owner>
   <summary>
     The success or error code for the setup of a CUPS printer. Recorded when
     setup is attempted through the settings dialogs. Only recorded on Chrome OS.