LibHTML: Add the outline of a CSS stylesheet object graph.

LibHTML/CSS/Selector.h

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <AK/AKString.h>
+#include <AK/Vector.h>
+
+class Selector {
+public:
+    Selector();
+    ~Selector();
+
+    struct Component {
+        enum class Type { Invalid, TagName, Id, Class };
+        Type type { Type::Invalid };
+        String value;
+    };
+
+    const Vector<Component>& components() const { return m_components; }
+
+private:
+    Vector<Component> m_components;
+};