[Sheriff] Mark flaky test on windows.

It was marked as flaky on linux nosnap, arm and nacl before. Now it's marked universally flaky since windows joined the list.

BUG=v8:2921
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/54713002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17506 ce2b1a6d-e550-0410-aec6-3dcde31c8c00