LibWeb: Extract the InnerHTML IDL mixin

Author: https://github.com/AtkinsSJ
Commit: https://github.com/SerenityOS/serenity/commit/200e111af0
Pull-request: https://github.com/SerenityOS/serenity/pull/14716
Reviewed-by: https://github.com/kennethmyhra
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibWeb/DOM/Element.idl

@@ -1,6 +1,7 @@
 #import <CSS/CSSStyleDeclaration.idl>
 #import <DOM/ChildNode.idl>
 #import <DOM/DOMTokenList.idl>
+#import <DOM/InnerHTML.idl>
 #import <DOM/NamedNodeMap.idl>
 #import <DOM/Node.idl>
 #import <DOM/NodeList.idl>
@@ -29,9 +30,6 @@ interface Element : Node {
     HTMLCollection getElementsByTagNameNS(DOMString? namespace, DOMString localName);
     HTMLCollection getElementsByClassName(DOMString className);
 
-    // FIXME: This should come from a InnerHTML mixin.
-    [LegacyNullToEmptyString, CEReactions] attribute DOMString innerHTML;
-
     [Reflect] attribute DOMString id;
     [Reflect=class] attribute DOMString className;
     [SameObject, PutForwards=value] readonly attribute DOMTokenList classList;

Userland/Libraries/LibWeb/DOM/InnerHTML.idl

@@ -0,0 +1,7 @@
+// https://w3c.github.io/DOM-Parsing/#the-innerhtml-mixin
+interface mixin InnerHTML {
+    [LegacyNullToEmptyString, CEReactions] attribute DOMString innerHTML;
+};
+
+Element includes InnerHTML;
+ShadowRoot includes InnerHTML;

Userland/Libraries/LibWeb/DOM/ShadowRoot.idl

@@ -1,11 +1,15 @@
 #import <DOM/DocumentFragment.idl>
+#import <DOM/InnerHTML.idl>
 
+// https://dom.spec.whatwg.org/#shadowroot
 interface ShadowRoot : DocumentFragment {
-
+    // FIXME: mode should return a ShadowRootMode
     readonly attribute DOMString mode;
+    // FIXME: readonly attribute boolean delegatesFocus;
+    // FIXME: readonly attribute SlotAssignmentMode slotAssignment;
     readonly attribute Element host;
-
-    // FIXME: This should come from a InnerHTML mixin.
-    [LegacyNullToEmptyString] attribute DOMString innerHTML;
-
+    // FIXME: attribute EventHandler onslotchange;
 };
+
+enum ShadowRootMode { "open", "closed" };
+enum SlotAssignmentMode { "manual", "named" };