Add stkhapugin as ios/c/b/ui/omnibox OWNER.

Adds stkhapugin as ios/chrome/browser/ui/omnibox OWNER.

Bug: None
Cq-Include-Trybots: luci.chromium.try:ios-simulator-full-configs;master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: I1743135f6fa395a240fe63bd528b46d5480ff280
Reviewed-on: https://chromium-review.googlesource.com/1154533Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579017}

ios/chrome/browser/ui/omnibox/OWNERS

 justincohen@chromium.org
 rohitrao@chromium.org
+stkhapugin@chromium.org
 jdonnelly@chromium.org
 
 # COMPONENT: UI>Browser>Omnibox