They should have done it long time ago. The pages today contain a lot of third-party scripts (advertisement, tracking, etc) and they sometimes can use up to 100

They should have done it long time ago. The pages today contain a lot of third-party scripts (advertisement, tracking, etc) and they sometimes can use up to 100% of a CPU core. Mobile browsers are already stopping background pages because otherwise the phone's battery would be drained in hours. Unless a background page is doing something useful for user, it should not consume any CPU time.