Google eBooks now work on Google Chrome browsers when a user if offline.
Xinixing Gu, Google Books Product Manager, explains in a blog post, “We’ve all been there: the Internet is suddenly down, and you can’t keep on reading your ebook to see what the character decides to do next. Or you’re about to head to the airport and want to be able to dive into a newly-purchased ebook during a long flight.”
To read Google eBooks offline, you have to install the Google Books app from the Chrome Web Store. Follow this link for a step-by-step guide on how to make sure your eBooks are accessible.