arc: Add owners and extend Arc.Secondary.Signin.Result

This one is important to estimate health of secondary account sign-in.
This stats should also be used for estimation of secondary account
sign-in improvements.

BUG=1036943
BUG=b:/146792085
TEST=N/A

Change-Id: I80c2ec4886fcaad79cb1de07899c01e2a9f9b997
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980897
Commit-Queue: Yury Khmel <khmel@chromium.org>
Auto-Submit: Yury Khmel <khmel@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Kush Sinha <sinhak@chromium.org>
Cr-Commit-Position: refs/heads/master@{#734099}

tools/metrics/histograms/histograms.xml

@@ -7586,7 +7586,9 @@ uploading your change for review.
 </histogram>
 
 <histogram name="Arc.Secondary.Signin.Result" enum="ArcProvisioningResult"
-    expires_after="2020-06-28">
+    expires_after="2020-12-31">
+  <owner>sinhak@google.com</owner>
+  <owner>jhorwich@google.com</owner>
   <owner>khmel@google.com</owner>
   <summary>
     The result (success or the type of failure) of ARC Secondary Account signin/