Although the fact that it stays completely black in your case might suggest you have another issue, I would still take a look at number six here, which solved my suspend issues:
Problem: Suspend-and-resume generates a stream of errors ...
ehci-pci 0000:00:1d.0: port 1 resume error -19
ehci-pci 0000:00:1d.0: port 2 resume error -19
usb usb3-port1: over-current condition
usb usb3-port1: connect-debounce failed
usb usb3-port2: over-current condition
usb usb3-port2: connect-debounce failed
... and blocks the Chromebook from executing a proper restart/shutdown.
case $1/$2 in
# Unbind ehci for preventing error
echo -n "0000:00:1d.0" | tee /sys/bus/pci/drivers/ehci-pci/unbind
# Bind ehci for preventing error
echo -n "0000:00:1d.0" | tee /sys/bus/pci/drivers/ehci-pci/bind
... and make it executable ...
$ sudo chmod 755 /lib/systemd/system-sleep/ehci-pci.sh
Configure boot options in /etc/default/grub ...
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash tpm_tis.force=1"
... save the changes and run ...
$ sudo update-grub
Suspend now works reliably when triggered from Ubuntu's shutdown menu or closing the lid and will resume the system with the desktop locked and a password prompt.