Don't let the GC clear the cache between cache invocations to pass test.

BUG=
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/17218005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@15233 ce2b1a6d-e550-0410-aec6-3dcde31c8c00