ADD AX role for Output Element
The html spec requires the output element be mapped to role=status
http://goo.gl/Fe89Dh

BUG=323143

Review URL: https://codereview.chromium.org/663783002

git-svn-id: svn://svn.chromium.org/blink/trunk@183939 bbb929c8-8fbe-4397-9dbb-9b2b20218538