With slices string string type removed generating a large amount of sub-strings takes more time. Change a test to avoid timeout in debug mode.
Review URL: http://codereview.chromium.org/385006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3260 ce2b1a6d-e550-0410-aec6-3dcde31c8c00