Ctrl-Alt-T  -- start a terminal
Ctrl-Alt-Shift-Refresh
  https://www.reddit.com/r/chromeos/comments/19k55e/
          
Force reboot -- Power and reload (circular arrow)
Factory reset
  https://support.google.com/chromebook/answer/183084
  Ctrl-Alt-Shift-r
reset 
  https://support.google.com/chromebook/answer/3227606
recover your chromebook
  https://support.google.com/chromebook/answer/1080595
Powerwash
  http://productforums.google.com/forum/#!msg/chromebook-central/dhL9ADpLj8c/0i7ivBCDKAAJ
  http://www.makeuseof.com/tag/two-ways-to-reformat-your-chromebook-powerwash-full-recovery/
Powerwash via Developer mode
  http://productforums.google.com/forum/#!msg/chromebook-central/dhL9ADpLj8c/0i7ivBCDKAAJ
  https://howtogeek.com/210817/how-to-enable-developer-mode-on-your-chromebook/
  https://productforums.google.com/forum/#!topic/chromebook-central/gekrx8_fZVs