The Apple Windows implementation is not able to load ResourceRequest objects that were created using "file://" URLs. This was happening because CFNetwork does not determine the MIME type of a file URL, and our CFNetwork backend would set a default MIME Type of "application/octet-stream", which would then be rejected by our loading logic.
Resolving this bug revealed another issue related to the URL class. This is documented under Bug 148598.
Created attachment 260331 [details]
Committed r189200: <http://trac.webkit.org/changeset/189200>