LibWeb: Add index and length into HTML::History

Author: https://github.com/kalenikaliaksandr
Commit: 40cbe9e72b
Pull-request: https://github.com/SerenityOS/serenity/pull/21209
Issue: https://github.com/SerenityOS/serenity/issues/21185
Reviewed-by: https://github.com/ADKaster ✅

Userland/Libraries/LibWeb/HTML/History.h

@@ -27,6 +27,9 @@ public:
     WebIDL::ExceptionOr<void> forward();
     WebIDL::ExceptionOr<u64> length() const;
 
+    u64 m_index { 0 };
+    u64 m_length { 0 };
+
 private:
     History(JS::Realm&, DOM::Document&);