Disable extra checks in Release mode.

They caused test failures and performance regressions.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/16158002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14856 ce2b1a6d-e550-0410-aec6-3dcde31c8c00