Array literal boilerplate objects can be transitioned while existing
un-transitioned clones are still being populated. This adds a check that
prevents us from performing the same transition twice.

R=danno@chromium.org
BUG=v8:2055
TEST=mjsunit/regress/regress-2055

Review URL: https://chromiumcodereview.appspot.com/9950095

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11221 ce2b1a6d-e550-0410-aec6-3dcde31c8c00