add handling for favicon link elements

fixes #6166

components/compositing/compositor.rs

@@ -454,6 +454,10 @@ impl<Window: WindowMethods> IOCompositor<Window> {
                 self.composite_if_necessary(CompositingReason::Headless);
             }
 
+            (Msg::NewFavicon(url), ShutdownState::NotShuttingDown) => {
+                self.window.set_favicon(url);
+            }
+
             // When we are shutting_down, we need to avoid performing operations
             // such as Paint that may crash because we have begun tearing down
             // the rest of our resources.