Add OWNERS for the SmokeTests file.

TBR=abarth@chromium.org, peter@chromium.org
BUG=289883

Review URL: https://chromiumcodereview.appspot.com/24207003

git-svn-id: svn://svn.chromium.org/blink/trunk@158069 bbb929c8-8fbe-4397-9dbb-9b2b20218538