URLRequestContextGetter is deprecated, and should no longer be used. New code should be written to work with the NetworkService instead, which may be out of process.  It looks like this code just uses the URLRequestContextGetter to get a thread (?) for reasons that are unclear to me.  I'm unsure whether the UI thread should be passed in instead when the network service is disabled (When it's enabled, too?), or if there's something else that needs to be done.