Claim ownership of GCM.UnregistrationRequestStatus UMA metric.

BUG=

Review URL: https://codereview.chromium.org/453103002

Cr-Commit-Position: refs/heads/master@{#288489}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@288489 0039d316-1c4b-4281-b951-d872f2087c98

tools/metrics/histograms/histograms.xml

@@ -8804,7 +8804,7 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 
 <histogram name="GCM.UnregistrationRequestStatus"
     enum="GCMUnregistrationRequestStatus">
-  <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
+  <owner>juyik@chromium.org</owner>
   <summary>Status code of the outcome of a GCM unregistration request.</summary>
 </histogram>