Add predictable mode to test driver.

BUG=391747
LOG=n
R=ishell@chromium.org

Review URL: https://codereview.chromium.org/371363003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22285 ce2b1a6d-e550-0410-aec6-3dcde31c8c00