switching to a linked representation of copied elements.  This change
avoids initializing frame elements to invalid unless they need to be.

Review URL: http://codereview.chromium.org/48008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1519 ce2b1a6d-e550-0410-aec6-3dcde31c8c00