Mark accessibility/chromium-only-roles.html as failing.

It looks like this test needs to be rebaselined after the changes in
https://crrev.com/303364 are fully implemented.

BUG=384723
TBR=yhirano@chromium.org

Review URL: https://codereview.chromium.org/708103003

git-svn-id: svn://svn.chromium.org/blink/trunk@185002 bbb929c8-8fbe-4397-9dbb-9b2b20218538