In r271879 I removed the support for data URLs in the network process for soup, assuming data URLs were always loaded from the web process, but that's not the case for downloads. I think we should not go to the network process for downloads either, but for now it's easier to fix this regression by supporting data URLs in the network process again. This was caught by http/tests/security/anchor-download-allow-data.html
Created attachment 418714 [details] Patch
Committed r272138: <https://trac.webkit.org/changeset/272138>