LibWeb: Parse CSS :host selector

Let's at least parse it, even if we don't implement matching for it yet.

Userland/Libraries/LibWeb/CSS/Parser/Parser.cpp

@@ -534,6 +534,8 @@ Parser::ParseErrorOr<Selector::SimpleSelector> Parser::parse_pseudo_simple_selec
             return make_pseudo_class_selector(Selector::SimpleSelector::PseudoClass::Type::OnlyOfType);
         if (pseudo_name.equals_ignoring_ascii_case("root"sv))
             return make_pseudo_class_selector(Selector::SimpleSelector::PseudoClass::Type::Root);
+        if (pseudo_name.equals_ignoring_ascii_case("host"sv))
+            return make_pseudo_class_selector(Selector::SimpleSelector::PseudoClass::Type::Host);
         if (pseudo_name.equals_ignoring_ascii_case("visited"sv))
             return make_pseudo_class_selector(Selector::SimpleSelector::PseudoClass::Type::Visited);
         if (pseudo_name.equals_ignoring_ascii_case("scope"sv))

Userland/Libraries/LibWeb/CSS/Selector.cpp

@@ -220,6 +220,7 @@ ErrorOr<String> Selector::SimpleSelector::serialize() const
         case Selector::SimpleSelector::PseudoClass::Type::OnlyChild:
         case Selector::SimpleSelector::PseudoClass::Type::Empty:
         case Selector::SimpleSelector::PseudoClass::Type::Root:
+        case Selector::SimpleSelector::PseudoClass::Type::Host:
         case Selector::SimpleSelector::PseudoClass::Type::FirstOfType:
         case Selector::SimpleSelector::PseudoClass::Type::LastOfType:
         case Selector::SimpleSelector::PseudoClass::Type::OnlyOfType:

Userland/Libraries/LibWeb/CSS/Selector.h

@@ -98,6 +98,7 @@ public:
                 NthLastChild,
                 Empty,
                 Root,
+                Host,
                 FirstOfType,
                 LastOfType,
                 OnlyOfType,
@@ -265,6 +266,8 @@ constexpr StringView pseudo_class_name(Selector::SimpleSelector::PseudoClass::Ty
         return "empty"sv;
     case Selector::SimpleSelector::PseudoClass::Type::Root:
         return "root"sv;
+    case Selector::SimpleSelector::PseudoClass::Type::Host:
+        return "host"sv;
     case Selector::SimpleSelector::PseudoClass::Type::FirstOfType:
         return "first-of-type"sv;
     case Selector::SimpleSelector::PseudoClass::Type::LastOfType:

Userland/Libraries/LibWeb/CSS/SelectorEngine.cpp

@@ -245,6 +245,9 @@ static inline bool matches_pseudo_class(CSS::Selector::SimpleSelector::PseudoCla
     }
     case CSS::Selector::SimpleSelector::PseudoClass::Type::Root:
         return is<HTML::HTMLHtmlElement>(element);
+    case CSS::Selector::SimpleSelector::PseudoClass::Type::Host:
+        // FIXME: Implement :host selector.
+        return false;
     case CSS::Selector::SimpleSelector::PseudoClass::Type::Scope:
         return scope ? &element == scope : is<HTML::HTMLHtmlElement>(element);
     case CSS::Selector::SimpleSelector::PseudoClass::Type::FirstOfType:

Userland/Libraries/LibWeb/Dump.cpp

@@ -467,6 +467,9 @@ void dump_selector(StringBuilder& builder, CSS::Selector const& selector)
                 case CSS::Selector::SimpleSelector::PseudoClass::Type::Root:
                     pseudo_class_description = "Root";
                     break;
+                case CSS::Selector::SimpleSelector::PseudoClass::Type::Host:
+                    pseudo_class_description = "Host";
+                    break;
                 case CSS::Selector::SimpleSelector::PseudoClass::Type::FirstOfType:
                     pseudo_class_description = "FirstOfType";
                     break;