Prefetch img and scripts during parsing

components/net_traits/lib.rs

@@ -237,6 +237,18 @@ impl FetchTaskTarget for IpcSender<FetchResponseMsg> {
     }
 }
 
+impl FetchTaskTarget for () {
+    fn process_request_body(&mut self, _: &Request) {}
+
+    fn process_request_eof(&mut self, _: &Request) {}
+
+    fn process_response(&mut self, _: &Response) {}
+
+    fn process_response_chunk(&mut self, _: Vec<u8>) {}
+
+    fn process_response_eof(&mut self, _: &Response) {}
+}
+
 pub trait Action<Listener> {
     fn process(self, listener: &mut Listener);
 }
@@ -368,6 +380,9 @@ pub enum FetchChannels {
         event_sender: IpcSender<WebSocketNetworkEvent>,
         action_receiver: IpcReceiver<WebSocketDomAction>,
     },
+    /// If the fetch is just being done to populate the cache,
+    /// not because the data is needed now.
+    Prefetch,
 }
 
 #[derive(Debug, Deserialize, Serialize)]