Which Bootloader is Used on a Chromebook?

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http://unix.stackexchange.com – I installed ChrUbuntu on an Acer C7 Chromebook, and I am able to dual boot Ubuntu 12.04 and ChromeOS and to control which OS loads by default. I tried to edit the /etc/default/grub file and did run update-grub successfully but saw no effects. I was trying to enable a "dmesg" style verbose system loading screen instead of the quiet splash screen (during the Ubuntu boot). I suspect that GRUB is not the bootloader on the machine or is functioning as a fairly late secondary bootloader only on the Linux partition. I realize that the Chromebook is a fairly closed system tightly controlled by Google, (HowTos)