This adds a new Byte representation and support for zero-extended
loads in HLoadNamedField and truncated stores in HStoreNamedField.

R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/25696004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17079 ce2b1a6d-e550-0410-aec6-3dcde31c8c00