Add missing include to timers

Library function close() needs unistd.h header included.

BUG=
R=jochen@chromium.org

Review URL: https://codereview.chromium.org/368363003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22228 ce2b1a6d-e550-0410-aec6-3dcde31c8c00