Make sure polymorphic element access creates non-replaying phis.

R=danno@chromium.org
BUG=v8:2815

Review URL: https://codereview.chromium.org/22589005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16136 ce2b1a6d-e550-0410-aec6-3dcde31c8c00