Make auto_roll run with a pure git checkout.

BUG=410721
LOG=n
TBR=jarin@chromium.org

Review URL: https://codereview.chromium.org/540513002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23672 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Refactor common unit test code.

TEST=compiler-unittests
BUG=v8:3489
LOG=n
R=svenpanne@chromium.org

Review URL: https://codereview.chromium.org/540823002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23673 ce2b1a6d-e550-0410-aec6-3dcde31c8c00