Rebaseline accessibility/chromium-only-roles.html

This test was disabled because of changes related to html hr tag were in progress. But now those changes are complete, hence we can enable this layout test.

BUG=384723

Review URL: https://codereview.chromium.org/721753004

git-svn-id: svn://svn.chromium.org/blink/trunk@185273 bbb929c8-8fbe-4397-9dbb-9b2b20218538