Previously all PyStats inheritted from JsonSerializable. The AbstractStat class has been added to give a cleaner, clearer Base class for PyStats. Change-Id: I7e1808c4b4dcd6110fd524ad3553a9dc19f72e24 Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/63691 Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu> Maintainer: Bobby Bruce <bbruce@ucdavis.edu> Tested-by: kokoro <noreply+kokoro@google.com>