external strings so that they are not disposed when running other
tests that rely on only one external string being disposed during its
run.

TBR=kasperl
Review URL: http://codereview.chromium.org/118158

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2095 ce2b1a6d-e550-0410-aec6-3dcde31c8c00