With the advent of the network service, we're planning on removing the ability to create bifurcated URLRequestContexts that share everything but the disk cache.  Only Chrome and Chromecast currently use this ability.

Fortunately, Chromecast just uses it to disable caching media media requests, so all we need to do is attach the LOAD_DISABLE_CACHE load flag to media requests, and we can then remove Chromecast's media URLRequestContext without altering behavior.