Google has updated their Google eBooks web app for the Chrome web browser.
Google Chrome would now cache the eBooks for offline reading.
Google eBooks now supports offline reading in Google Chrome. Whether you are flying through the air, backpacking through the European countryside, or simply facing intermittent network connections, you can always read your Google eBooks in your Chrome browser or on your Chromebook.
This feature would only work if you have the Google Books web app installed in your Chrome browser and turned on the syncing functionality.