Interceptor.Chain is missing protocols

[edechamps-Google]

#9108 made it possible for Interceptors to access various OkHttpClient options from Interceptor.Chain.

However, it is not possible to access OkHttpClient.protocols in this way, as there is no accessor for it.

This presents a problem when implementing "transport" interceptors that wish to take over the Call and run it themselves (as opposed to passing it down OkHttp's stack), which is what we are trying to do. Such an interceptor would want to know which protocols are allowed.

@yschimke @vkasprov

[seanxuu]

I’d like to investigate this issue. I plan to check whether exposing the client’s configured protocols through Interceptor.Chain is compatible with OkHttp’s API design, then add focused tests for transport interceptors. I’ll keep the change minimal and wait for maintainer feedback before implementing it.

[yschimke]

@seanxuu it isn't really something appropriate for someone picking up.