LibWeb: Implement Performance.toJSON

Author: https://github.com/jamierocks
Commit: 66c3388b16
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/682
Reviewed-by: https://github.com/tcl3 ✅

Userland/Libraries/LibWeb/HighResolutionTime/Performance.idl

@@ -13,6 +13,7 @@ typedef sequence<PerformanceEntry> PerformanceEntryList;
 interface Performance : EventTarget {
     DOMHighResTimeStamp now();
     readonly attribute DOMHighResTimeStamp timeOrigin;
+    [Default] object toJSON();
 
     readonly attribute PerformanceTiming timing;