[vm] Print isolate group metrics when an isolate shuts down.
[vm] Print isolate group metrics when an isolate shuts down.

These metrics used to be printed because they were isolate metrics.

Should fix Golem's use of --print_metrics.

Change-Id: Ib427aab5f1b4d589f7c7c55295e8128a5fbb1745
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/136816
Reviewed-by: Alexander Aprelev <dfb74c35a357c2059971a4bf7fe26b6a7c18085d@google.com>
Reviewed-by: Martin Kustermann <a35dd5b79fac84b2bb3b026a16b8becc55af5961@google.com>
Commit-Queue: Ryan Macnak <d738b7f001baf9789095d7dc549cff6de60b011d@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk