In my own work, when I fork threads that are run and executed by the kernel, I still make decisions outside the kernel about how those threads run. I may tell threads to go to sleep, wait for another thread to finish something, or prefer a certain thread to run over others.

Yes, they are still scheduled by the OS kernel, but they are also being controlled by my own scheduling algorithms. I call this scheduling, because it's the same problem as OS level scheduling. And if I have to do it, I imagine Chrome has to do it. In this scenario, if you want to understand the runtime behavior of the threads, you must consider both OS kernel level decisions and my scheduling decisions.

I would also be surprised if there was no Chrome memory management inbetween malloc and the OS kernel.