Update Plugin VM histogram expiry and OWNERS

This CL updates expiry and OWNERS for:
PluginVm.Image.DownloadedSize
PluginVm.LaunchResult
PluginVm.SetupResult
PluginVm.SetupTime

The new expiry date is about 6 months out and matches
PluginVm.SetupFailureReason. We still want to track these metrics so we
can keep track of how the Plugin VM install/launch is going.

Bug: 1149503
Change-Id: I0ebd76a3496d2dd2d3f2471feb40eb095e7164e8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2563338Reviewed-by: Olya Kalitova <okalitova@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Timothy Loh <timloh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833187}

tools/metrics/histograms/histograms_xml/plugin/histograms.xml

@@ -178,8 +178,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="PluginVm.Image.DownloadedSize" units="MB"
-    expires_after="2020-12-31">
-  <owner>aoldemeier@chromium.org</owner>
+    expires_after="2021-05-16">
+  <owner>joelhockey@chromium.org</owner>
   <owner>okalitova@chromium.org</owner>
   <owner>timloh@chromium.org</owner>
   <summary>
@@ -189,8 +189,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 </histogram>
 
 <histogram name="PluginVm.LaunchResult" enum="PluginVmLaunchResult"
-    expires_after="2020-12-31">
-  <owner>aoldemeier@chromium.org</owner>
+    expires_after="2021-05-16">
+  <owner>joelhockey@chromium.org</owner>
   <owner>okalitova@chromium.org</owner>
   <owner>timloh@chromium.org</owner>
   <summary>
@@ -208,7 +208,7 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
 
 <histogram name="PluginVm.SetupResult" enum="PluginVmSetupResult"
     expires_after="2021-05-16">
-  <owner>aoldemeier@chromium.org</owner>
+  <owner>joelhockey@chromium.org</owner>
   <owner>okalitova@chromium.org</owner>
   <owner>timloh@chromium.org</owner>
   <summary>
@@ -218,8 +218,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   </summary>
 </histogram>
 
-<histogram name="PluginVm.SetupTime" units="ms" expires_after="2020-12-31">
-  <owner>aoldemeier@chromium.org</owner>
+<histogram name="PluginVm.SetupTime" units="ms" expires_after="2021-05-16">
+  <owner>joelhockey@chromium.org</owner>
   <owner>okalitova@chromium.org</owner>
   <owner>timloh@chromium.org</owner>
   <summary>