set referrer in window.load_url

- this conforms to follow-hyperlinks spec step 13
- this conforms to window-open spec step 14.3
- replace uses of `referrer_url` with `referrer`
- in Request class, change "no-referrer" to ""
- set websocket fetch referrer to "no-referrer"

components/script/dom/window.rs

@@ -87,6 +87,7 @@ use js::rust::HandleValue;
 use msg::constellation_msg::PipelineId;
 use net_traits::image_cache::{ImageCache, ImageResponder, ImageResponse};
 use net_traits::image_cache::{PendingImageId, PendingImageResponse};
+use net_traits::request::Referrer;
 use net_traits::storage_thread::StorageType;
 use net_traits::{ReferrerPolicy, ResourceThreads};
 use num_traits::ToPrimitive;
@@ -1716,6 +1717,7 @@ impl Window {
         url: ServoUrl,
         replace: bool,
         force_reload: bool,
+        referrer: Referrer,
         referrer_policy: Option<ReferrerPolicy>,
     ) {
         let doc = self.Document();
@@ -1781,7 +1783,7 @@ impl Window {
             self.main_thread_script_chan()
                 .send(MainThreadScriptMsg::Navigate(
                     pipeline_id,
-                    LoadData::new(url, Some(pipeline_id), referrer_policy, Some(doc.url())),
+                    LoadData::new(url, Some(pipeline_id), Some(referrer), referrer_policy),
                     replace,
                 ))
                 .unwrap();