LibWeb: Remove a bunch of redundant Document::navigable() lookups

Document::navigable() can be unpleasantly slow, since we don't have a
direct link between documents and navigables at the moment. So let's not
call it twice when once is enough.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -1042,8 +1042,9 @@ void Document::update_layout()
 
     // NOTE: If our parent document needs a relayout, we must do that *first*.
     //       This is necessary as the parent layout may cause our viewport to change.
-    if (navigable() && navigable()->container())
-        navigable()->container()->document().update_layout();
+    auto navigable = this->navigable();
+    if (navigable && navigable->container())
+        navigable->container()->document().update_layout();
 
     update_style();
 
@@ -1054,7 +1055,7 @@ void Document::update_layout()
     if (m_created_for_appropriate_template_contents)
         return;
 
-    if (!navigable())
+    if (!navigable)
         return;
 
     auto viewport_rect = this->viewport_rect();
@@ -1097,10 +1098,10 @@ void Document::update_layout()
     // Broadcast the current viewport rect to any new paintables, so they know whether they're visible or not.
     inform_all_viewport_clients_about_the_current_viewport_rect();
 
-    navigable()->set_needs_display();
+    navigable->set_needs_display();
     set_needs_to_resolve_paint_only_properties();
 
-    if (navigable()->is_traversable()) {
+    if (navigable->is_traversable()) {
         // NOTE: The assignment of scroll frames only needs to occur for traversables because they take care of all
         //       nested navigable documents.
         paintable()->assign_scroll_frames();
@@ -2120,9 +2121,10 @@ void Document::update_readiness(HTML::DocumentReadyState readiness_value)
     dispatch_event(Event::create(realm(), HTML::EventNames::readystatechange));
 
     if (readiness_value == HTML::DocumentReadyState::Complete) {
-        if (navigable() && navigable()->is_traversable()) {
+        auto navigable = this->navigable();
+        if (navigable && navigable->is_traversable()) {
             HTML::HTMLLinkElement::load_fallback_favicon_if_needed(*this).release_value_but_fixme_should_propagate_errors();
-            navigable()->traversable_navigable()->page().client().page_did_finish_loading(url());
+            navigable->traversable_navigable()->page().client().page_did_finish_loading(url());
         } else {
             m_needs_to_call_page_did_load = true;
         }
@@ -2275,7 +2277,8 @@ bool Document::is_fully_active() const
 
 bool Document::is_active() const
 {
-    return navigable() && navigable()->active_document() == this;
+    auto navigable = this->navigable();
+    return navigable && navigable->active_document() == this;
 }
 
 // https://html.spec.whatwg.org/multipage/history.html#dom-document-location

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -922,8 +922,9 @@ JS::NonnullGCPtr<Geometry::DOMRectList> Element::get_client_rects() const
     // FIXME: - Replace each anonymous block box with its child box(es) and repeat this until no anonymous block boxes
     //          are left in the final list.
     const_cast<Document&>(document()).update_layout();
-    VERIFY(document().navigable());
-    auto viewport_offset = document().navigable()->viewport_scroll_offset();
+    auto navigable = document().navigable();
+    VERIFY(navigable);
+    auto viewport_offset = navigable->viewport_scroll_offset();
 
     if (document().paintable()) {
         // NOTE: Make sure CSS transforms are resolved before it is used to calculate the rect position.

Userland/Libraries/LibWeb/HTML/EventLoop/EventLoop.cpp

@@ -158,7 +158,8 @@ void EventLoop::process()
 
     // 2. Rendering opportunities: Remove from docs all Document objects whose node navigables do not have a rendering opportunity.
     docs.remove_all_matching([&](auto& document) {
-        return document->navigable() && !document->navigable()->has_a_rendering_opportunity();
+        auto navigable = document->navigable();
+        return navigable && !navigable->has_a_rendering_opportunity();
     });
 
     // 3. If docs is not empty, then set hasARenderingOpportunity to true
@@ -254,7 +255,8 @@ void EventLoop::process()
 
     // 16. For each fully active Document in docs, update the rendering or user interface of that Document and its browsing context to reflect the current state.
     for_each_fully_active_document_in_docs([&](DOM::Document& document) {
-        if (document.navigable() && document.navigable()->needs_repaint()) {
+        auto navigable = document.navigable();
+        if (navigable && navigable->needs_repaint()) {
             auto* browsing_context = document.browsing_context();
             auto& page = browsing_context->page();
             page.client().schedule_repaint();

Userland/Libraries/LibWeb/HTML/HTMLTitleElement.cpp

@@ -29,8 +29,9 @@ void HTMLTitleElement::initialize(JS::Realm& realm)
 void HTMLTitleElement::children_changed()
 {
     HTMLElement::children_changed();
-    if (navigable() && navigable()->is_traversable()) {
-        navigable()->traversable_navigable()->page().client().page_did_change_title(document().title().to_byte_string());
+    auto navigable = this->navigable();
+    if (navigable && navigable->is_traversable()) {
+        navigable->traversable_navigable()->page().client().page_did_change_title(document().title().to_byte_string());
     }
 }