Since our zap values are valid heap object addreses we might hit asserts if a heap object gets the value of a zap constant as its address. 

Review URL: http://codereview.chromium.org/6456022

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6695 ce2b1a6d-e550-0410-aec6-3dcde31c8c00