Constants can still change their representation, so we cannot determine reachability of blocks based on their Smi-ness

BUG=chromium:351320
LOG=y
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/196943002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19836 ce2b1a6d-e550-0410-aec6-3dcde31c8c00