The biggest impact it will have is that core/fetch/FetchContext.h interface and it's implementation in core/loader/FrameFetchContext.{h,cpp} will get a bit bigger, will core/fetch/ResourceFetcher.{h,cpp} get smaller.
I've already done a bit of cleanup in core/css and core/xml so that they get access to a Document pointer directly, rather than using ResourceFetcher::document(). I think that's the main API change, at least in terms of how the rest of core/ perceives core/fetch/.
Some classes may also be moved around, particularly between core/fetch/ and core/loader. These directories were historically one very broad directory, and the division we created was incomplete. I'm trying to ensure core/loader/ is primarily navigation concepts and core/fetch/ is primarily generic resource loading concepts.
~Nate