Crashes if rax doesn't point to readable memory.
Recent change made rax contain garbage due to write-barrier computation.
(The fact that it hasn't crashed before highly suggests that the line does nothing.)

Review URL: http://codereview.chromium.org/545117

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3644 ce2b1a6d-e550-0410-aec6-3dcde31c8c00