LibWeb: Port {HTML,UIEvents,XHR}::EventNames to new String

Author: https://github.com/kennethmyhra
Commit: 4d87072201
Pull-request: https://github.com/SerenityOS/serenity/pull/17825
Reviewed-by: https://github.com/linusg ✅
Reviewed-by: https://github.com/trflynn89

Userland/Libraries/LibWeb/HTML/HTMLFrameSetElement.cpp

@@ -38,7 +38,7 @@ void HTMLFrameSetElement::parse_attribute(DeprecatedFlyString const& name, Depre
 #undef __ENUMERATE
 }
 
-DOM::EventTarget& HTMLFrameSetElement::global_event_handlers_to_event_target(DeprecatedFlyString const& event_name)
+DOM::EventTarget& HTMLFrameSetElement::global_event_handlers_to_event_target(FlyString const& event_name)
 {
     // NOTE: This is a little weird, but IIUC document.body.onload actually refers to window.onload
     // NOTE: document.body can return either a HTMLBodyElement or HTMLFrameSetElement, so both these elements must support this mapping.