LibWeb: Add the ResizeObserverBoxOptions IDL enum

Author: https://github.com/IdanHo
Commit: 61fc3c31c6
Pull-request: https://github.com/SerenityOS/serenity/pull/13424
Reviewed-by: https://github.com/alimpfard ✅

Userland/Libraries/LibWeb/ResizeObserver/ResizeObserver.idl

@@ -12,9 +12,10 @@ interface ResizeObserver {
 
 callback ResizeObserverCallback = void (sequence<ResizeObserverEntry> entries, ResizeObserver observer);
 
-dictionary ResizeObserverOptions {
-
-    // FIXME: This should be an enum.
-    DOMString box = "content-box";
-
+enum ResizeObserverBoxOptions {
+    "border-box", "content-box", "device-pixel-content-box"
+};
+
+dictionary ResizeObserverOptions {
+    ResizeObserverBoxOptions box = "content-box";
 };