Can you spot it in Autoruns? I still say, it has to be in Autoruns or it isn't a startup issue. Chrome must do it after the boot, then, after you click it to run. After you close Chrome, the stuff sticks around a bit to be there just in case you open Chrome again. It likely would unload as soon as the RAM is needed by something else.
Or, maybe you're right that prefetch is at fault. That article I found says how to temporarily turn it off to see.