Intel-based Chromebooks have long been using U-Boot as a payload for Coreboot while now all of that support is going upstream. A commit today adds U-Boot as a possible payload for x86 systems when configured via the new Kconfig options.
The commit by Google's Martin Roth explains, "Graphics worked in U-Boot correctly by initializing the VBIOS and setting up a console mode. Tested in QEMU and on Minnowboard Max."
If you are unfamiliar with the different Coreboot payload options, see more via this Wikipedia section.