LibWeb: Make Element::tag_name() return a const FlyString&

The more generic virtual variant is renamed to node_name() and now only
Element has tag_name(). This removes a huge amount of String ctor/dtor
churn in selector matching.

Libraries/LibWeb/Bindings/NodeWrapper.cpp

@@ -55,7 +55,7 @@ NodeWrapper* wrap(JS::Heap& heap, Node& node)
 NodeWrapper::NodeWrapper(Node& node)
     : EventTargetWrapper(node)
 {
-    put("nodeName", JS::js_string(heap(), node.tag_name()));
+    put("nodeName", JS::js_string(heap(), node.node_name()));
 }
 
 NodeWrapper::~NodeWrapper()

Libraries/LibWeb/DOM/Comment.h

@@ -36,7 +36,7 @@ public:
     explicit Comment(Document&, const String&);
     virtual ~Comment() override;
 
-    virtual FlyString tag_name() const override { return "#comment"; }
+    virtual FlyString node_name() const override { return "#comment"; }
 };
 
 template<>

Libraries/LibWeb/DOM/Document.h

@@ -69,7 +69,7 @@ public:
     CSS::StyleSheetList& style_sheets() { return *m_style_sheets; }
     const CSS::StyleSheetList& style_sheets() const { return *m_style_sheets; }
 
-    virtual FlyString tag_name() const override { return "#document"; }
+    virtual FlyString node_name() const override { return "#document"; }
 
     void set_hovered_node(Node*);
     Node* hovered_node() { return m_hovered_node; }

Libraries/LibWeb/DOM/DocumentFragment.h

@@ -41,7 +41,7 @@ public:
     {
     }
 
-    virtual FlyString tag_name() const override { return "#document-fragment"; }
+    virtual FlyString node_name() const override { return "#document-fragment"; }
 };
 
 template<>

Libraries/LibWeb/DOM/DocumentType.h

@@ -36,7 +36,7 @@ public:
     explicit DocumentType(Document&);
     virtual ~DocumentType() override;
 
-    virtual FlyString tag_name() const override { return "#doctype"; }
+    virtual FlyString node_name() const override { return "#doctype"; }
 
     const String& name() const { return m_name; }
     void set_name(const String& name) { m_name = name; }

Libraries/LibWeb/DOM/Element.h

@@ -45,7 +45,8 @@ public:
     Element(Document&, const FlyString& tag_name);
     virtual ~Element() override;
 
-    virtual FlyString tag_name() const final { return m_tag_name; }
+    virtual FlyString node_name() const final { return m_tag_name; }
+    const FlyString& tag_name() const { return m_tag_name; }
 
     bool has_attribute(const FlyString& name) const { return !attribute(name).is_null(); }
     String attribute(const FlyString& name) const;

Libraries/LibWeb/DOM/Node.h

@@ -84,7 +84,7 @@ public:
 
     virtual RefPtr<LayoutNode> create_layout_node(const StyleProperties* parent_style) const;
 
-    virtual FlyString tag_name() const = 0;
+    virtual FlyString node_name() const = 0;
 
     virtual String text_content() const;
 

Libraries/LibWeb/DOM/Text.h

@@ -37,7 +37,7 @@ public:
     explicit Text(Document&, const String&);
     virtual ~Text() override;
 
-    virtual FlyString tag_name() const override { return "#text"; }
+    virtual FlyString node_name() const override { return "#text"; }
 
 private:
     virtual RefPtr<LayoutNode> create_layout_node(const StyleProperties* parent_style) const override;

Libraries/LibWeb/DOMTreeModel.cpp

@@ -130,7 +130,7 @@ GUI::Variant DOMTreeModel::data(const GUI::ModelIndex& index, Role role) const
         if (node.is_text())
             return String::format("%s", with_whitespace_collapsed(to<Text>(node).data()).characters());
         if (!node.is_element())
-            return node.tag_name();
+            return node.node_name();
         auto& element = to<Element>(node);
         StringBuilder builder;
         builder.append('<');

Libraries/LibWeb/Layout/StackingContext.cpp

@@ -65,7 +65,7 @@ void StackingContext::dump(int indent) const
 {
     for (int i = 0; i < indent; ++i)
         dbgprintf(" ");
-    dbgprintf("SC for %s{%s} %s [children: %zu]\n", m_box.class_name(), m_box.node() ? m_box.node()->tag_name().characters() : "(anonymous)", m_box.absolute_rect().to_string().characters(), m_children.size());
+    dbgprintf("SC for %s{%s} %s [children: %zu]\n", m_box.class_name(), m_box.node() ? m_box.node()->node_name().characters() : "(anonymous)", m_box.absolute_rect().to_string().characters(), m_children.size());
     for (auto& child : m_children)
         child->dump(indent + 1);
 }

Libraries/LibWeb/LayoutTreeModel.cpp

@@ -134,7 +134,7 @@ GUI::Variant LayoutTreeModel::data(const GUI::ModelIndex& index, Role role) cons
         if (node.is_anonymous()) {
             builder.append("[anonymous]");
         } else if (!node.node()->is_element()) {
-            builder.append(node.node()->tag_name());
+            builder.append(node.node()->node_name());
         } else {
             auto& element = to<Element>(*node.node());
             builder.append('<');

Libraries/LibWeb/Parser/HTMLParser.cpp

@@ -194,7 +194,7 @@ static bool parse_html_document(const StringView& html, Document& document, Pare
         case State::Free:
             if (ch == '<') {
                 bool should_treat_as_text = false;
-                if (node_stack.last().tag_name() == "script") {
+                if (node_stack.last().node_name() == "script") {
                     bool is_script_close_tag = peek(1) == '/'
                         && tolower(peek(2)) == 's'
                         && tolower(peek(3)) == 'c'