ladybird/Libraries/LibWeb/NavigationTiming/PerformanceExtensions.idl

// https://w3c.github.io/navigation-timing/#extensions-to-the-performance-interface
[Exposed=Window]
partial interface Performance {
    [SameObject]
    readonly attribute PerformanceTiming timing;
    [SameObject]
    readonly attribute PerformanceNavigation navigation;
};