LibWeb: Implement 'fetch timing info' struct

Author: https://github.com/linusg
Commit: fef331a03f
Pull-request: https://github.com/SerenityOS/serenity/pull/15795
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/davidot ✅

Userland/Libraries/LibWeb/Forward.h

@@ -193,6 +193,7 @@ namespace Web::Fetch::Infrastructure {
 class Body;
 struct BodyWithType;
 class ConnectionTimingInfo;
+class FetchTimingInfo;
 struct Header;
 class HeaderList;
 class Request;