I tried to breed with golden carrots horses in an enclosed space surrounded by stone fence and with open fence gates in front of them. One horse in each stall, beside each other. When I gave each one a golden carrot I faced the direction it was looking. No hearts appeared (I had particles on) then the horses walked out of their stalls and a foal appeared between them. Originally however I had just been feeding them because they were a little damaged, and this occurred after they were at full health. The one horse had been around since at least 1.9. Sorry I couldn't get a screenshot.