All of this works well for me for hibernating to file, thanks for the instructions! In my case I also had to get the latest stable kernel for hibernate to file to work, i.e. Ubuntu 17.10 and a dell xps 9370, I had to upgrade the kernel to 4.16.0rc
Note that if hibernating to file, you still have to do the whole filefrag stuff to copy the physical_offset to the etc/default/grub file,e.g. GRUB_CMD_LINUX_DEFAULT="quiet splash resume=swap_file_deb_partition resume_offset=physical_offset_as_filefrag_says" and then do not forget to run sudo update-grup and reboot for changes to take effect!