I would expect kernels to be quite small (#file, line-count) compared to major Applications like Unreal Games and Civilization 5. I've never worked on Chrome, but I can safely say the amount of source code in a few Unreal Games and Civilization5 dwarfs the drivers and OS code I've worked on. Take Unreal then add a team of developers adding onto it for multiple years thru multiple releases. Then add all the middleware (Havok, AudioEngines, NaturalMotion).

OS are much larger than kernel, I'd guess all the driver code exceeds the actual kernel.

People always think they code base is large, but having built most of the Call of Duties and many Unreal games, all the OS code I've worked on is trivial in size comparison. There is probably something bigger, but games seem bigger than many major apps in my experience.