over the frame elements to find registers used (before allocating
undetermined elements) and another pass to set the frame's register
indices (after allocating all elements).
Review URL: http://codereview.chromium.org/114018

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1906 ce2b1a6d-e550-0410-aec6-3dcde31c8c00