Chrome Version: 61
Chrome OS Version: 61
Chrome OS Platform: all

See design doc: 
https://docs.google.com/a/google.com/document/d/1g5pCclqYzjbSbcEupIfaADYEzbk5jotEv1RUgh3sKNM/edit?usp=sharing

excerpt from doc of the objective:

Our goal is to ensure that tab discarding happens as quickly as possible when the Chrome OS system is experiencing severe memory pressure and remove timer-based polling from Chrome.  This requires implementing multiple levels of memory pressure notification in the kernel and having Chrome use the select() system calls (or equivalently poll()) for asynchronous notification.

The main purpose of this is to improve behavior of Chrome OS systems under low-memory conditions.