Service workers and blob urls after installing custom url handler

URLRequestContextGetterQt::generateJobFactory() was not originally designed to be called more than once. We do however call it again now when custom URLs are changed on an already live profile.

However both the blob protocol handler and the Chromium' requestIntercepts are handed over to be owned by the jobfactory, and are no longer available second time generateJobFactory is called.

The request intercepters are used by service workers and app-cache.