Chrome Version       : Version 53.0.2785.101 (ubuntu 15.04 64-bit)
URLs (if applicable) :outlook.com, facebook.com(users logged out)
Other browsers tested:Nil
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:Nil
     Safari:
    Firefox:
         IE:

What steps will reproduce the problem?
(1) Browser was running in the background.
(2) watching video on laptop in the foreground



What is the expected result?
system should have been stable.

What happens instead?
suddenly, happened to see black screen with some logs related to acpi and lock screen appeared.


Please confirm if this is an issue.

Please provide any additional information below. Attach a screenshot if
possible.