we store an AllocationSiteInfo object right after the JSArray, with a pointer to the
boilerplate object. Later, if the array transitions we check for the continued existence
of the temporary AllocationSiteInfo object (has no roots). If found, we'll use it to
transition the boilerplate array as well.

Danno's original changeset: https://codereview.chromium.org/10615002/

Review URL: https://codereview.chromium.org/11663005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13330 ce2b1a6d-e550-0410-aec6-3dcde31c8c00