make the concept of has_listeners_for follow other implementations

components/script/dom/document.rs

@@ -1665,7 +1665,7 @@ impl Document {
         let event = beforeunload_event.upcast::<Event>();
         event.set_trusted(true);
         let event_target = self.window.upcast::<EventTarget>();
-        let has_listeners = event.has_listeners_for(&event_target, &atom!("beforeunload"));
+        let has_listeners = event_target.has_listeners_for(&atom!("beforeunload"));
         event_target.dispatch_event_with_target(
             document.root().upcast(),
             &event,
@@ -1738,7 +1738,7 @@ impl Document {
             );
             event.set_trusted(true);
             let event_target = self.window.upcast::<EventTarget>();
-            let has_listeners = event.has_listeners_for(&event_target, &atom!("unload"));
+            let has_listeners = event_target.has_listeners_for(&atom!("unload"));
             let _ = event_target.dispatch_event_with_target(
                 document.root().upcast(),
                 &event,

components/script/dom/event.rs

@@ -103,16 +103,6 @@ impl Event {
         self.cancelable.set(cancelable);
     }
 
-    // Determine if there are any listeners for a given target and type.
-    // See https://github.com/whatwg/dom/issues/453
-    pub fn has_listeners_for(&self, target: &EventTarget, type_: &Atom) -> bool {
-        // TODO: take 'removed' into account? Not implemented in Servo yet.
-        // https://dom.spec.whatwg.org/#event-listener-removed
-        let mut event_path = self.construct_event_path(&target);
-        event_path.push(DomRoot::from_ref(target));
-        event_path.iter().any(|target| target.has_listeners_for(type_))
-    }
-
     // https://dom.spec.whatwg.org/#event-path
     fn construct_event_path(&self, target: &EventTarget) -> Vec<DomRoot<EventTarget>> {
         let mut event_path = vec![];

components/script/dom/eventtarget.rs

@@ -309,6 +309,8 @@ impl EventTarget {
         Ok(EventTarget::new(global))
     }
 
+    // Determine if there are any listeners for a given event type.
+    // See https://github.com/whatwg/dom/issues/453
     pub fn has_listeners_for(&self,
                              type_: &Atom)
                              -> bool {