Add kbr to Source/web/OWNERS.

We're debugging Timer-related issues in the Blink/Chromium boundary.
I'm a Source/core OWNER and would like to be able to LGTM patches in
this area.

BUG=393331,408358
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/514193003

git-svn-id: svn://svn.chromium.org/blink/trunk@181061 bbb929c8-8fbe-4397-9dbb-9b2b20218538