ROOT-A : 5 GB : ext2
STATE : about 30 GB or more : ext4
Note down the partition numbers. Example:
ROOT-A : /dev/sda7
STATE : /dev/sda8
Use a fast enough USB drive and burn ArnoldTheBat's chromium image in it using Etcher or any other software.
Mount the ROOT-A and STATE partitions on hard disk and also from the USB drive. Copy all files from ROOT-A of USB drive to ROOT-A of hard disk. Similarly for STATE.
From the link to XDA thread, download chromefy.sh script, eve and caroline images. Unpack the zips in the same directory (say ~/Downloads).
From step-1 see the ROOT-A partition number. For me it was /dev/sda7. Substitute it in the following commands as needed.
ROOT_PARTITION="/dev/sda7"
cd </path/to/chromefy+chromeos_images>
sudo bash ./chromefy.sh $ROOT_PARTITION <chromeos_eve_image.bin> <chromeos_caroline_recovery_image.bin>
Important
If you are told that the partition was previously mounted and if you would like to continue, hit n.
Go to nautilus (or any other file manager) and mount the ROOT-A partition
cd /media/<username>/<name_of_ROOT-A_partition_in_hdd>/usr/sbin
sudo cp write_gpt.sh write_gpt.sh.bak
sudo gedit write_gpt.sh
Search for base_vars and partition_vars. Edit the partition numbers of ROOT-A and STATE from step-1 and remove all other partition information. The size of ROOT-A and STATE need not be altered.
Save the file and maintain a copy of it.
sudo cp /media/<username>/<name_of_ROOT-A_partition_in_hdd>/usr/sbin/write_gpt.sh /home/<username>/
sudo update-grub
An entry "Chrome (on /dev/sdaX)" should be now present in GRUB entry.
Navigate to /boot/grub and edit the grub.cfg file.
sudo gedit /boot/grub/grub.cfg
Search for "Chrome" and add cros_debug in the end of the following line as shown:
linux /boot/vmlinuz-4.14.67 root=/dev/sda7 cros_debug
This should preferably be in the main menuentry.