This change replaces WebState's `*WebUI` related methods with ones that allow storing a set of WebUI's such that WebUI's can create child frames that also load WebUI which can be necessary for untrusted frames.
This change replaces WebState's `*WebUI` related methods with ones that allow storing a set of WebUI's such that WebUI's can create child frames that also load WebUI which can be necessary for untrusted frames.