Switch DEPS to git.

BUG=415464
LOG=n
R=agable@chromium.org

Review URL: https://codereview.chromium.org/702113002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25274 ce2b1a6d-e550-0410-aec6-3dcde31c8c00