Hosts file for Chromebook?

There are two options available:

1) Edit the hosts file from a Developer Chromebook:

sudo /usr/share/vboot/bin/make_dev_ssd.sh --remove_rootfs_verification --partitions 2

You will lose changes to the hosts file when ChromeOS does update again. Updates can be disabled by creating the file /mnt/stateful_partition/etc/lsb-release that contains the following 2 lines:

CHROMEOS_RELEASE_VERSION=9999.9999.9999.9999
GOOGLE_RELEASE=9999.9999.9999.9999

2) Using a Chrome extension

This topic is discussed thoroughly in this question: Simulate manipulation of the etc/hosts file in Google Chrome -- it is debated as to whether any of the extensions actually work the same as a hosts file modification.

Unfortunately, I do not know either how to modify the host file without disabling the auto-update functionality, but depending on what you want to use that host file for, you could try installing a Chrome extension that has similar functionality as the host file.

For instance, there is Block Site for making your own list of sites you want to block. There is AdBlock Plus for blocking ads. And there is Rescue Time Dashboard for keeping track of which sites you spend most of your time on.

If you want to change your hosts file so you can point back to 127.0.0.1 then can I suggest http://readme.localtest.me/.