At this point, you can unmount the partitions and reboot the computer to (hopefully) boot into Arch. ArChr contains a "linux-chromeboot" package, which contains kernel modules, as well as a "chromeboot" package, which contains the following boot utilities:
"chromeboot" - run "chromeboot chrome" to make the system boot Chrome OS; run "chromeboot linux" to make the system boot Arch. Use "chromeboot linux once" to start linux only on the next boot.
"chromeboot-update" - updates the command-line parameters for the Arch kernel. Config is stored in /etc/chromeboot.conf; edit that first, then call this script to apply it.
"cgpt" and "vbutil_kern" from Chrome OS. Others like "crossystem" and "set_gbb_flags.sh" are copied if it can find them.