Add Chromium metrics OWNERS as OWNERS of api/uma_metrics.h

As requested on bugs.webrtc.org/12096#c2, this CL adds a Chromium
metric OWNERS in order to always have their review when WebRTC's UMA
metrics are updated.

Bug: webrtc:12096
Change-Id: Icd9ab7dda5f7a4ba6ac078f667c1fd39f3314123
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/191702
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#32728}
diff --git a/api/OWNERS b/api/OWNERS
index 4cf3915..afd95c6 100644
--- a/api/OWNERS
+++ b/api/OWNERS
@@ -12,3 +12,16 @@
 
 per-file DEPS=mbonadei@webrtc.org
 per-file DEPS=kwiberg@webrtc.org
+
+# Please keep this list in sync with Chromium's //base/metrics/OWNERS and
+# send a CL when you notice any difference.
+# Even if people in the list below cannot formally grant +1 on WebRTC, it
+# is good to get their LGTM before sending the CL to one of the folder OWNERS.
+per-file uma_metrics.h=asvitkine@chromium.org
+per-file uma_metrics.h=bcwhite@chromium.org
+per-file uma_metrics.h=caitlinfischer@google.com
+per-file uma_metrics.h=holte@chromium.org
+per-file uma_metrics.h=isherman@chromium.org
+per-file uma_metrics.h=jwd@chromium.org
+per-file uma_metrics.h=mpearson@chromium.org
+per-file uma_metrics.h=rkaplow@chromium.org