Allow removal of obsolete map checks after transitions.

This allows side effect dominator tracking to remove map checks that are
dominated by a single HStoreNamedField that performs a transition on the
same object. A similar trick could be applied to HAllocateObject.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/12035026

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@13488 ce2b1a6d-e550-0410-aec6-3dcde31c8c00