This is because allocation folding can cause uninitialized and hence uniterable fragments. Trying to inspect them causes SizeFromMap() crashes.

R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/467693002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23084 ce2b1a6d-e550-0410-aec6-3dcde31c8c00