title: How to detect when daydream starts/ends
body: <p>In jellybeam mr2 daydream replaced display sleep. An application was able to know when the sleep starts or ends by registering broadcast receiver for action ACTION_SCREEN_ON, ACTION_SCREEN_OFF. Is there any way to do the same against daydream? </p>
  
  <p>Just to be clear, I'm not trying to add a new daydream service, but just want to be informed of (any) daydream-related events.</p>