Volley currently depends on Apache HTTP. We can mostly remove the dependency except that HttpStack#performRequest returns an org.apache.http.HttpResponse, which means it'd be an API-breaking change to remove.

It might be worth biting the bullet and just doing a major version bump that breaks the API. There are other known issues that we could potentially address alongside this. However, one avenue worth exploring would be to see if we could treat Apache HTTP as a "provided" dependency - that is, one which is available at compile time, but not runtime - and then deprecate the old performRequest and add a new one that is implemented by all built-in clients (except HttpClientStack, which should be deprecated as well).

I think the result would compile and let apps build against Volley without pulling in the Apache HTTP dependency, but existing users could continue to use the Apache stack as long as they pulled in the dependency at runtime (and it should be there on an actual Android device).

Apart from the ugliness, my main concern is how proguard would respond to the missing reference - we could add a consumer proguard rule to not warn on org.apache stuff though that might be a bit overbearing.