Enter realms when creating special same-origin iframes.

components/script/dom/servoparser/mod.rs

@@ -919,6 +919,7 @@ impl FetchResponseListener for ParserContext {
         if parser.aborted.get() {
             return;
         }
+        let _realm = enter_realm(&*parser);
         parser.parse_bytes_chunk(payload);
     }
 
@@ -934,6 +935,8 @@ impl FetchResponseListener for ParserContext {
             return;
         }
 
+        let _realm = enter_realm(&*parser);
+
         match status {
             // are we throwing this away or can we use it?
             Ok(_) => (),

components/script/script_thread.rs

@@ -1649,6 +1649,7 @@ impl ScriptThread {
             // https://html.spec.whatwg.org/multipage/#the-end step 6
             let mut docs = self.docs_with_no_blocking_loads.borrow_mut();
             for document in docs.iter() {
+                let _realm = enter_realm(&**document);
                 document.maybe_queue_document_completion();
             }
             docs.clear();