Comment 48 for bug 1530530

As mentioned, works in Ubuntu 16.10 and newer. The message is still there but can be bypassed.

Note that Mint is Ubuntu with small tweaks, so Mint 18 (built on Ubuntu 16.04) working probably means their live image creation uses something else than gfxboot for the first run menu. Fixing gfxboot would be the best option, since changing to something else could break other computers too. Ability to skip gfxboot would be nice though.

Before 16.10 I successfully did 16.04 installation by installing on another computer, and then transferring that installation to my Chromebook. Gfxboot is only used for Legacy boot's live session graphical menu, not for booting installed Ubuntu or for the UEFI live boot. So if any Chromebook gets non-Legacy boot working, also live image should boot without the error/warning message.

These are the options currently. Feel free to co-operate a final full fix to development Ubuntu or backporting the workaround possibility to 16.04.