Move js perf tests to a common root on the perf dashboard.

BUG=
R=dslomov@chromium.org

Review URL: https://codereview.chromium.org/667373004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@24806 ce2b1a6d-e550-0410-aec6-3dcde31c8c00