Function webkit2gtk_sys::webkit_website_data_manager_fetch

pub unsafe extern "C" fn webkit_website_data_manager_fetch(
    manager: *mut WebKitWebsiteDataManager, 
    types: WebKitWebsiteDataTypes, 
    cancellable: *mut GCancellable, 
    callback: GAsyncReadyCallback, 
    user_data: gpointer
)

This is supported on crate feature v2_16 only.