This type of decision is used when WebKit has received a response for a network resource and is about to start the load.
Note that these resources include all subresources of a page such as images and stylesheets as well as main documents. Appropriate policy responses to this decision are use, ignore, or download. This type of policy decision is always a ResponsePolicyDecision. This decision is useful for forcing some types of resources to be downloaded rather than rendered in the WebView or to block the transfer of resources entirely.