Add an OWNERS file for browser_context_keyed_service component.

Based on chrome/browser/profiles/OWNERS.

BUG=227219
R=erg@chromium.org, mirandac@chromium.org, rlp@chromium.org

Review URL: https://codereview.chromium.org/16114006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@202945 0039d316-1c4b-4281-b951-d872f2087c98

components/browser_context_keyed_service/OWNERS

+erg@chromium.org
+mirandac@chromium.org
+phajdan.jr@chromium.org
+rlp@chromium.org