Add a fetch recipe for infra_internal.

Although many things are private, the urls of the infra_internal and
build_internal repositories are not. So let's just add a fetch recipe
for them anyway.

R=iannucci@chromium.org

Review URL: https://codereview.chromium.org/544863006

git-svn-id: http://src.chromium.org/chrome/trunk/tools/depot_tools@292586 4ff67af0-8c30-449e-8e8b-ad334ec8d88c