[Sheriff] DevTools: Skip virtual/implsidepainting/inspector/timeline/timeline-paint.html on Mac.

BUG=none
TBR= caseq@chromium.org, arv@chromium.org

Review URL: https://codereview.chromium.org/24629002

git-svn-id: svn://svn.chromium.org/blink/trunk@158334 bbb929c8-8fbe-4397-9dbb-9b2b20218538