Android is 90% Java frameworks. C and C++ applications are only allowed to use these libraries from the underlying OS.

https://developer.android.com/ndk/guides/stable_apis.html

Trying to link to anything else will terminate the application, starting with Android 7.

https://developer.android.com/about/versions/nougat/android-...

ChromeOS is a browser based OS, that happens to have Linux underneath.

On Android Things, the NDK is even more constrained to the point that the device drivers API is mostly exposed via Java.

https://developer.android.com/things/sdk/index.html

In all cases, their fork of Linux has some POSIX API removed.

http://www.cs.columbia.edu/~vatlidak/resources/POSIXmagazine...

So, Google could tomorrow replace Linux by anything else and only OEMs writing drivers would notice.

Which is actually what they are doing with their Fuchsia project.

https://github.com/fuchsia-mirror