Further improve old space allocation write barrier elimination.

Stores to old space allocations require no write barriers if the
object is the new space dominator and the value is not in new space.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/290173003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21360 ce2b1a6d-e550-0410-aec6-3dcde31c8c00