DumpRenderTree has not been functional under WinCairo for the better part of a year. I finally tracked the cause down to the use of 'mutableCopy' for resource requests in the DumpRenderTree logic.
This attached patch provides an implementation of this logic for the cURL-based WinCairo port so that DumpRenderTree works properly again.
Created attachment 90441 [details]
Landed in http://trac.webkit.org/changeset/84435.