(Kinuko: added a separate bug for this to track the effort)
(this is from comment #132 in parent bug)


We (jam@, scottmg@, ananta@ and kinuko@) discussed how URLLoader{Factory,} could be set up for a main resource for navigation, and here's a rough note:

Some basic facts:
- For main resources it's possible that, say, a request goes to SW -> network -> (redirect) -> SW
- The lifetime of the navigation request / NavigationURLLoader and that of URLLoader can be different, as a single request may talk to multiple URLLoader(Factory)
- We can't tell which URLLoader(Factory) will serve the final request beforehand, and resolution could happen asyncly
- In redirects we'll need to restart the process, and some redirect contexts / states will need to be kept around across redirect legs

High-level possible design:
- When we start a request we initialize a chain of URLLoaderFactory in NavigationURLLoader
- Each feature's URLLoaderFactory may forward the request to the next URLLoaderFactory in the chain if it finds it can't handle it
- In redirect case the request will start from the beginning of the chain
- Each feature may keep track the redirect/restart state during the request (e.g. in their own request_handlers in SW and AppCache cases, at least initially)
- We could have URLLoaderFactoryManager or something to keep/manage all these factories and states during the lifetime of the navigation request