Remove the checks.h dependence on logging.h in a standalone build.

logging.h apparently drags in a lot of undesirable dependencies. It was
only required for the trivial LogMessageVoidify; simply add an
identical FatalMessageVoidify instead.

Keep the include in a Chromium build to still have the override
mechanism use Chromium's macros.

Bonus: Add the missing DCHECK_GT (noticed by bercic).

R=kwiberg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/17259004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7031 4adac7df-926f-26a2-2b94-8c16560cd09d