Why didn't Dumbledore tell Harry that Snape was going to kill him?

Why didn't Dumbledore tell Harry that Snape was going to kill him?

I do realise that this would be a very harsh thing to say to Harry, however, wouldn't it of made it easier for Harry in the end? If the knew that Snape was really a good person. Did he not tell Harry because Severus asked Dumbledore to not reveal the best of him? Did he not speak of it because he didn't want that information falling into the wrong hands?