content/dom: set navigator.onLine attribute to true (#36560)

Sets the navigator.onLine attribute to true.

Testing:
Ran `./mach run https://pinterest.com
--enable-experimental-web-platform-features`. This doesn't show the
"Hmm..you're not connected to the internet" text anymore.
<img width="1027" alt="Screenshot 2025-04-16 at 11 31 02 AM"
src="https://github.com/user-attachments/assets/3745077b-dc51-42ce-88a0-38d5f157fc0c"
/>


part of: #36554

---------

Signed-off-by: Siddhant N. Trivedi <sidntrivedi012@gmail.com>
Signed-off-by: Siddhant N Trivedi <sidntrivedi012@gmail.com>
Co-authored-by: Josh Matthews <josh@joshmatthews.net>

components/script/dom/navigator.rs

@@ -222,6 +222,11 @@ impl NavigatorMethods<crate::DomTypeHolder> for Navigator {
         to_frozen_array(&[self.Language()], cx, retval, can_gc)
     }
 
+    /// <https://html.spec.whatwg.org/multipage/#dom-navigator-online>
+    fn OnLine(&self) -> bool {
+        true
+    }
+
     // https://html.spec.whatwg.org/multipage/#dom-navigator-plugins
     fn Plugins(&self) -> DomRoot<PluginArray> {
         self.plugins

components/script/dom/workernavigator.rs

@@ -105,6 +105,11 @@ impl WorkerNavigatorMethods<crate::DomTypeHolder> for WorkerNavigator {
         to_frozen_array(&[self.Language()], cx, retval, can_gc)
     }
 
+    /// <https://html.spec.whatwg.org/multipage/#dom-navigator-online>
+    fn OnLine(&self) -> bool {
+        true
+    }
+
     // https://w3c.github.io/permissions/#navigator-and-workernavigator-extension
     fn Permissions(&self) -> DomRoot<Permissions> {
         self.permissions