Add expected failure for fast/sub-pixel/ellipsis-zoom.html after r155341

TBR=cbiesinger@chromium.or

Review URL: https://codereview.chromium.org/21635002

git-svn-id: svn://svn.chromium.org/blink/trunk@155360 bbb929c8-8fbe-4397-9dbb-9b2b20218538