Improve UX when the timeline events for a frame are not available

Sometimes, selecting a frame in the Frames chart that doesn't have Timeline Events shows a toast in the bottom right:

Steps to reproduce:
1. Run an app in profile mode and connect to DevTools
2. Trigger some frames
3. Refresh the DevTools web application
4. Select a frame that was gathered before the refresh
5. See toast message

Instead, I would like some indication where the Timeline Events chart is displayed that tells me there are no timeline events for this frame, and that I should trigger some new frames and maybe avoid refreshing the page. Right now the Timeline Events chart will either show no frame data or the frame data for the previous frame that was selected. Instead, maybe this could be greyed out to indicate that there's a problem.

Riproduci il problema tramite il Frames chart e verifica come risponde il Timeline Events chart dopo aver selezionato un frame raccolto prima dell’aggiornamento. Il lavoro è completato quando gli eventi della timeline non disponibili vengono indicati nell’area del grafico, invece di mostrare dati obsoleti o solo un toast, con indicazioni per attivare nuovi frames ed evitare l’aggiornamento.

Scritto dal modello di indicizzazione a partire dal testo della issue.