LibWeb: Implement document-tree child navigable target name property set

This AO allows accessing child navigables by their name as named
properties on the WindowProxy object.

Tests/LibWeb/Text/expected/HTML/Window-named-properties-iframe.txt

@@ -0,0 +1,2 @@
+   true
+true

Tests/LibWeb/Text/input/HTML/Window-named-properties-iframe.html

@@ -0,0 +1,12 @@
+<script src="../include.js"></script>
+<iframe name="framey" src=""></iframe>
+<iframe name=spices></iframe>
+<script>
+    test(() => {
+        println(window.framey === window.frames[0]);
+        println(window.spices == window.frames[1]);
+
+        // FIXME: Test with cross-origin iframe?
+        // FIXME: Test with iframe that sets window.name -- this changes nothing atm
+    });
+</script>

Userland/Libraries/LibWeb/HTML/Window.cpp

@@ -1395,4 +1395,46 @@ JS::NonnullGCPtr<CustomElementRegistry> Window::custom_elements()
     return JS::NonnullGCPtr { *m_custom_element_registry };
 }
 
+// https://html.spec.whatwg.org/#document-tree-child-navigable-target-name-property-set
+OrderedHashMap<String, JS::NonnullGCPtr<Navigable>> Window::document_tree_child_navigable_target_name_property_set()
+{
+    // The document-tree child navigable target name property set of a Window object window is the return value of running these steps:
+
+    // 1. Let children be the document-tree child navigables of window's associated Document.
+    auto children = associated_document().document_tree_child_navigables();
+
+    // 2. Let firstNamedChildren be an empty ordered set.
+    OrderedHashMap<String, JS::NonnullGCPtr<Navigable>> first_named_children;
+
+    // 3. For each navigable of children:
+    for (auto const& navigable : children) {
+        // 1. Let name be navigable's target name.
+        auto const& name = navigable->target_name();
+
+        // 2. If name is the empty string, then continue.
+        if (name.is_empty())
+            continue;
+
+        // 3. If firstNamedChildren contains a navigable whose target name is name, then continue.
+        if (first_named_children.contains(name))
+            continue;
+
+        // 4. Append navigable to firstNamedChildren.
+        (void)first_named_children.set(name, *navigable);
+    }
+
+    // 4. Let names be an empty ordered set.
+    OrderedHashMap<String, JS::NonnullGCPtr<Navigable>> names;
+
+    // 5. For each navigable of firstNamedChildren:
+    for (auto const& [name, navigable] : first_named_children) {
+        // 1. Let name be navigable's target name.
+        // 2. If navigable's active document's origin is same origin with window's relevant settings object's origin, then append name to names.
+        if (navigable->active_document()->origin().is_same_origin(relevant_settings_object(*this).origin()))
+            names.set(name, *navigable);
+    }
+
+    return names;
+}
+
 }

Userland/Libraries/LibWeb/HTML/Window.h

@@ -191,6 +191,8 @@ public:
 
     static void set_internals_object_exposed(bool);
 
+    [[nodiscard]] OrderedHashMap<String, JS::NonnullGCPtr<Navigable>> document_tree_child_navigable_target_name_property_set();
+
 private:
     explicit Window(JS::Realm&);
 

Userland/Libraries/LibWeb/HTML/WindowProxy.cpp

@@ -113,10 +113,11 @@ JS::ThrowCompletionOr<Optional<JS::PropertyDescriptor>> WindowProxy::internal_ge
     if (property.has_value())
         return property;
 
-    // FIXME: 6. If property is undefined and P is in W's document-tree child browsing context name property set, then:
-    if (false) {
-        // FIXME: 1. Let value be the WindowProxy object of the named object of W with the name P.
-        auto value = JS::js_undefined();
+    // 6. If property is undefined and P is in W's document-tree child navigable target name property set, then:
+    auto navigable_property_set = m_window->document_tree_child_navigable_target_name_property_set();
+    if (auto navigable = navigable_property_set.get(property_key.to_string().view()); navigable.has_value()) {
+        // 1. Let value be the active WindowProxy of the named object of W with the name P.
+        auto value = navigable.value()->active_window_proxy();
 
         // 2. Return PropertyDescriptor{ [[Value]]: value, [[Enumerable]]: false, [[Writable]]: false, [[Configurable]]: true }.
         // NOTE: The reason the property descriptors are non-enumerable, despite this mismatching the same-origin behavior, is for compatibility with existing web content. See issue #3183 for details.