First, you need to know where to get the right stuff. I installed straight on the device, so chrUbuntu was the obvious choice. It's a pretty nice script that allows you to do just about anything necessary.
1) Bring your Chromebook to developer mode.
I'm not going to give the details. It's findable on the Internet, and unsafe enough that you should only do this if you know what you're doing... That counts double for running Trusty on the Samsung Chromebook.
From there, get into crosh (Ctrl+Alt+T), in shell mode (type shell at the crosh prompt).
2) Download the script:
3) Run the script:
sudo bash s9ryd xubuntu-desktop dev
This will do the gory install step, partition your device and format the new partition, download the ubuntu core tarball, and from there install the metapackage you've asked for as a first argument.
Be aware that if you have never repartitioned the device, you'll likely notice the system rebooting during the process -- if that happens, just re-run the same command to pick this back up where they ended. It's clear when the process is done and the system installed -- the script requires you to press Enter to reboot.
This was where things got fun.
Turns out my device booted fine into Trusty, but it would only show a black screen with the mouse cursor. If you moved the mouse, you could see the cursor changing but still nothing else. Switching to another VT (Ctrl-Alt-arrow (F1) or whatnot) would work to get you a text-mode login, but only if you switched early enough while X was getting ready to load... otherwise, you'd just get a pretty garbled display.
I hacked at the whole thing for a good while. I already know xf86-video-armsoc was involved in ChromeOS at some point, so I tried to install that.
Still no love. Tried to copy the libs from ChromeOS to the device, in case it was some libmali or EGL/GLES issue... Still nothing better.
I even touched /etc/X11/xorg.conf with some black magic, looking up the details using w3m in a text console...
Turns out the problem was with xf86-video-armsoc itself. I initially clued in when I looked at the dates for upload of the X packages and xf86-video-armsoc itself -- it didn't seem quite right: X was newer by a bit. I knew there could be some issue with the ABI in some cases; but after more careful investigation, that's probably fine too -- armsoc properly depends on -abi-14.
After much more work and trial and error, I updated xf86-video-armsoc to 0.6.0 from the Linaro git tree and also reverted one commit changing flags and it's not mostly working. X runs, I get lightdm, I can run apps -- "compositing" in Xubuntu works too, to get transparency and gradients... all with some minimal display corruption of the window decorations.
So the end of the line is -- if you want to run Trusty on your Chromebook and run into similar black screen issues, and you feel daring, feel free to try my newly-built xf86-video-armsoc package in my PPA:
It's simple; once you're in a text console on the machine (login as user/user):
nmcli dev wifi connect <your wifi network> password <your wifi password>
sudo add-apt-repository ppa:mathieu-tl/ppa
sudo apt-get update
sudo apt-get install xserver-xorg-video-armsoc-exynos
These updated packages, or at least some kind of permanent fix, should make it into Trusty soon. Stay tuned :)