Currently synthesizes Smi as the lower bound for numeric operations (except for +, which might result in a string). That would need to change in places where we want to track constants as type feedback.

Does not do anything about variables yet.

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/17842004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15422 ce2b1a6d-e550-0410-aec6-3dcde31c8c00