[Sheriff] Temporarily mark test as flaky.

BUG=
TBR=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/145593002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18770 ce2b1a6d-e550-0410-aec6-3dcde31c8c00