Add 4 new core/OWNERS.

Some of these folks were nominated over a month ago
but we failed to add them after the 5 days passed.  Sorry.

Review URL: https://codereview.chromium.org/220963004

git-svn-id: svn://svn.chromium.org/blink/trunk@170907 bbb929c8-8fbe-4397-9dbb-9b2b20218538