Add Type::cast

R=danno@chromium.org
BUG=

Review URL: https://codereview.chromium.org/18843002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15551 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Unrevert "Derive synthetic type bounds for expressions"

Reenables https://codereview.chromium.org/17842004

R=jkummerow@chromium.org
BUG=

Review URL: https://codereview.chromium.org/18847002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15552 ce2b1a6d-e550-0410-aec6-3dcde31c8c00