ResourceLoader.h has two different callback methods.
On Mac - virtual NSCachedURLResponse* willCacheResponse(ResourceHandle*, NSCachedURLResponse*);
On Windows - virtual bool shouldCacheResponse(ResourceHandle*, CFCachedURLResponseRef);
The method on Windows should match the one on Mac. It should be
virtual CFCachedURLResponseRef willCacheResponse(ResourceHandle*, CFCachedURLResponseRef);
I am adding the above method for Mac when using CFNetwork (see bug 51836). Windows code should use that.