Similar to why I'm doing #9172, I'm changing `Rc<RefCell<Response>>` into `Rc<Response>` and wrapping fields in `RefCell<T>` as needed. So far I've only needed to change `url_list`, but I'm sure I'll need to update more fields in the future.
There's two lines that don't compile that I'm not going to bother trying to fix until #9172 is approved, because getting them to work now will just require more changes after merging with the changes #9172 makes to them.
Source-Repo: https://github.com/servo/servo
Source-Revision: b8186a2203cdbdcc24d77554cb53e048ef13c669
This puts them in a new file located at `net_traits/response.rs`.
Source-Repo: https://github.com/servo/servo
Source-Revision: 99689bc6b0531837f1af18ed4b7e4fd765595606