Called on the IO thread before a resource is loaded. The |browser| and
|frame| values represent the source of the request, and may be NULL for
requests originating from service workers or cef_urlrequest_t. To allow
the resource to load using the default network loader return NULL. To
specify a handler for the resource return a cef_resource_handler_t object.
The |request| object cannot not be modified in this callback.
Called on the IO thread before a resource is loaded. The |browser| and |frame| values represent the source of the request, and may be NULL for requests originating from service workers or cef_urlrequest_t. To allow the resource to load using the default network loader return NULL. To specify a handler for the resource return a cef_resource_handler_t object. The |request| object cannot not be modified in this callback.