New unified type representation

Not used yet, only unit tests.

R=jkummerow@chromium.org, svenpanne@chromium.org
BUG=

Review URL: https://codereview.chromium.org/16154027

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14957 ce2b1a6d-e550-0410-aec6-3dcde31c8c00