TODO(loading-dev): Write brief description about URLLoaderFactory, URLLoader and URLLoaderClient.
A deck that explains how Mojo connections for these URLLoader classes can be established to issue a network request with diagrams: https://docs.google.com/presentation/d/1ku7pkh09h6sQ6epudsVvHehRzvanAU7ckzfiVvMoljo/edit?usp=sharing