Currently, we can fail a resource request by either returning a nullptr Resource from ResourceFetcher::RequestResource, or by populating a Resource with an error.
https://chromium-review.googlesource.com/c/chromium/src/+/858257 will standardize all failures on a non-null Resource with an error.
This will likely enable some additional cleanup opportunities, once we can assume that there is only one failure codepath.
Comment 1 by bugdroid1@chromium.org
, Jan 23 2018