Websites can indicate that a particular Client Hint is critical to the page by including it in a `Critical-CH` HTTP response header. Doing so will trigger a connection restart if the hint listed in the `Critical-CH` HTTP response header could be (but wasn’t) included in the HTTP request initially sent. This intent proposes adding `readonly attribute DOMHighResTimeStamp criticalCHRestart;` to the `PerformanceNavigationTiming` interface.