Objects can actually be stored into themselves. This fails when no write
barrier is needed (eg, the object was just allocated).

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/148733005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@19095 ce2b1a6d-e550-0410-aec6-3dcde31c8c00