When used with d8 this can potentially interfer with the writing,
reading and deletion of files is the isolates flags makes the same
test run concurrently.
Review URL: http://codereview.chromium.org/7308006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8540 ce2b1a6d-e550-0410-aec6-3dcde31c8c00