Not just Linux, but ChromeOS is based on Gentoo Linux (originally Ubuntu); which is to say, much of the userspace stack was pre-exsting as well. The core of the operating system is the Chrome web browser, which was also a pre-exsting project, which a relatively clear business interest to Google (influence over the web platform).
Android has a bit of a better claim, as more of the userspace stack was written for it. It also wasn't started by Google (although they bought Android Inc. years before it was released publicly).
