Use autofocus on the correct element

R=ojan@chromium.org
NOTRY=true
BUG=404387

Review URL: https://codereview.chromium.org/480323003

git-svn-id: svn://svn.chromium.org/blink/trunk@180602 bbb929c8-8fbe-4397-9dbb-9b2b20218538