Discussion:

clamy ==>
It avoids a thread hop. On normal navigations I would very much argue that this is needed since it's on the critical path. In the prefetch case, not having the NavigationThrottle might just make the prefetch a bit slower to start.

droger ==>
Is the idea to move code from the PrerenderResourceThrottle to a NavigationThrottle?

If so, I'm not convinced there is much we can do, since our ResourceThrottle works on all resources, not only the navigation.

Or maybe the idea is not to move the code, but rather to share the code between ResourceThrottle and NavigationThrottle, so that they essentially do the same thing, but one works on subresources and the other on main resources?

clamy ==>
Yes that's the idea. You keep the ResourceThrottle for subresources & add a NavigationThrottle for main resources. As I mention this is a performance optimization that may make less sense on the prefetch though.