Install git with version >=1.7.7
https://github.com/git/git/releases
Install depot_tools
http://dev.chromium.org/developers/how-tos/install-depot-tools
Install help script
git clone https://chromium.googlesource.com/chromiumos/chromite
Initial sync
cros_mirror -r /mirror/git -u git://repo.zhenglei.net
Updating Sync
cros_mirror -r /mirror/git