Support CPU profiling for short lived isolates

Right now, this should be possible by selecting the isolate from the isolate selector, and then clicking "Load all CPU samples". This would only be possible if the following are true
- the isolate is still in the isolate selector after closing (unknown)
- the cpu samples for this isolate are still in the CPU sample buffer

Start with the isolate selector and the "Load all CPU samples" action. Check whether a short-lived isolate remains selectable after closing and whether its samples remain in the CPU sample buffer; done means those conditions support loading CPU samples for the closed isolate.

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