LibWeb: Update HTML fragment serialization for declarative shadow DOM

Author: https://github.com/awesomekling
Commit: e62db9c118
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/278
Reviewed-by: https://github.com/mattco98
Reviewed-by: https://github.com/nico

Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.h

@@ -61,7 +61,11 @@ public:
     DOM::Document& document();
 
     static Vector<JS::Handle<DOM::Node>> parse_html_fragment(DOM::Element& context_element, StringView);
-    static String serialize_html_fragment(DOM::Node const& node, DOM::FragmentSerializationMode = DOM::FragmentSerializationMode::Inner);
+    enum class SerializableShadowRoots {
+        No,
+        Yes,
+    };
+    static String serialize_html_fragment(DOM::Node const&, SerializableShadowRoots, Vector<JS::Handle<DOM::ShadowRoot>> const&, DOM::FragmentSerializationMode = DOM::FragmentSerializationMode::Inner);
 
     enum class InsertionMode {
 #define __ENUMERATE_INSERTION_MODE(mode) mode,