Session
Counts what happened to a set of sessions.
Owned by whoever created those sessions, not by the process. The counters used to live on PageSession's companion, which meant every session in the application shared them: a caller could not ask "how many of my sessions are open", and the instrumented suite could not either. Four device tests passed alone and failed together because each was reading the others' totals.
A session that is not given one gets its own, so nothing is shared by accident. Pass the same registry to several sessions to aggregate them.
Properties
Sessions currently initialised and not yet torn down.
Operations refused rather than risking an out-of-memory kill.
Renderer processes that died reporting a crash.
Renderer processes the system killed to reclaim memory.
Navigations and redirects refused by the SSRF rules.