LibWeb: Add a way to give DOM::Element a ShadowRoot

You can now attach a shadow root to your favorite Element. It doesn't
do anything yet, but you can.

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -31,8 +31,8 @@
 #include <LibWeb/CSS/StyleInvalidator.h>
 #include <LibWeb/CSS/StyleResolver.h>
 #include <LibWeb/DOM/Document.h>
-#include <LibWeb/DOM/DocumentFragment.h>
 #include <LibWeb/DOM/Element.h>
+#include <LibWeb/DOM/ShadowRoot.h>
 #include <LibWeb/DOM/Text.h>
 #include <LibWeb/HTML/Parser/HTMLDocumentParser.h>
 #include <LibWeb/Layout/BlockBox.h>
@@ -365,4 +365,12 @@ NonnullRefPtrVector<Element> Element::get_elements_by_class_name(const FlyString
     return elements;
 }
 
+void Element::set_shadow_root(RefPtr<ShadowRoot> shadow_root)
+{
+    if (m_shadow_root == shadow_root)
+        return;
+    m_shadow_root = move(shadow_root);
+    invalidate_style();
+}
+
 }

Userland/Libraries/LibWeb/DOM/Element.h

@@ -101,6 +101,10 @@ public:
     NonnullRefPtrVector<Element> get_elements_by_tag_name(const FlyString&) const;
     NonnullRefPtrVector<Element> get_elements_by_class_name(const FlyString&) const;
 
+    ShadowRoot* shadow_root() { return m_shadow_root; }
+    const ShadowRoot* shadow_root() const { return m_shadow_root; }
+    void set_shadow_root(RefPtr<ShadowRoot>);
+
 protected:
     RefPtr<Layout::Node> create_layout_node() override;
 
@@ -116,6 +120,8 @@ private:
     RefPtr<CSS::StyleProperties> m_specified_css_values;
 
     Vector<FlyString> m_classes;
+
+    RefPtr<ShadowRoot> m_shadow_root;
 };
 
 template<>