Right, GDAX is essentially the Coinbase pair exchange, as the only markets they offer mirror the Coinbase fiat exchanges - BTC, BCC, ETH, LTC. My guess is it gets rebranded as Coinbase at some point because Coinbase is by far and away the more well-known brand in that family.
Which again means, I don't think Coinbase has any particular use for Cointracking. I don't believe that any major exchange would, at least until a dominant exchange emerges in the coming years.