[Sheriff] Disable virtual/gpu/compositedscrolling/overflow/clear-scroll-parent.html on mac.

BUG=298039
TBR= vollick@chromium.org

Review URL: https://codereview.chromium.org/24536002

git-svn-id: svn://svn.chromium.org/blink/trunk@158309 bbb929c8-8fbe-4397-9dbb-9b2b20218538