[Sheriff] Revert "Check elimination temporarily disabled.", "Fix for buildbot failure after r19102." and "Check elimination improvement: propagation of state through phis is supported, CheckMap narrowing implemented."

This reverts commit r19102, r19105 and r19170 for breaking the
Chrome browser_tests. Will reland once fixed.

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/130053007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19179 ce2b1a6d-e550-0410-aec6-3dcde31c8c00