Gardening: virtual/softwarecompositing/rtl/rtl-iframe-absolute-overflow.html for rebaselines

This test consistently fails on the bots, but looks fine.

TBR=ccameron@chromium.org
BUG=338794

Review URL: https://codereview.chromium.org/306593002

git-svn-id: svn://svn.chromium.org/blink/trunk@174909 bbb929c8-8fbe-4397-9dbb-9b2b20218538