Similar to how Google added Android app support to Chrome OS, it seems Google is now planning to do the same with the still elusive Fuchsia OS. As identified by 9to5google, changes made to the Gerrit code confirm that Fuchsia OS will use a specialized version of the Android Runtime (ART) to run Android apps.
As an OS can be made or broken by its library of applications, it stands to reason that Google would want to hit the ground running on the application front. Fortunately, it has the most popular mobile OS with a huge library of apps in the Play Store. It seems as though Google plans to leverage this advantage if and when it decides to launch Fuchsia.
It remains unclear how ART will run in Fuchsia OS. It is possible that Google may use an approach similar to how the Linux subsystem works in Windows 10. In this method, the Fuchsia Kernel would replace Linux kernel calls with equivalent calls for its own kernel. Google may instead decide to run ART inside a virtual machine.
What remains even more elusive is if and when Google will officially release Fuchsia OS and a supporting device. However, if you're curious to see the OS in its early stages and you have a spare Pixelbook lying around, you can install Fuchsia OS on it or if you want to see Fuchsia in action you can check it out here.