Is the Chancellor + Harbinger combo a viable Dominion strategy?
This doesn't work as you are thinking:


Harbinger has you draw a card before you look through your discard pile. This means that when you play Harbinger, the first thing you do is draw a card, which requires you shuffle your discard pile and make a new draw deck. So having played Chancellor first actually makes Harbinger worthless!
Harbinger doesn't put the card into your hand like you said, it puts it on top of your deck.
Because Chancellor is a terminal action, and would need to be played before Harbinger, this requires that you first play a Village or another action that gives +2 Actions.
Even if it did work as you were thinking; the end result would be the 1 best card in your deck gets to get played sooner in the shuffle rather than later; or maybe played multiple times within 1 shuffle. This same thing is accomplished with both Scheme and Scavenger by themselves; instead of requiring a multiple card combo.
A minor point, but as Chancellor was removed from the second edition of Dominion, which is where Harbinger comes from; these 2 cards don't both exist in the same "Dominion world". Of course in casual play they are still both available; but it's likely that online play and tournaments won't have them both.