Garlic Butter: In small bowl, stir together butter, garlic, thyme, rosemary, salt and pepper.
Roast Chicken: Sprinkle cavity of chicken with salt and pepper; fill with onion, thyme and rosemary. Rub chicken all over with Garlic Butter. Place, breast side up, on greased rack in roasting pan.
Roast in 375°F (190°C) oven for 45 minutes; baste and continue to roast, basting occasionally, until instant-read thermometer inserted in thickest part of thigh reads 185°F (85°C), about 30 more minutes. Discard contents of cavity. Using tongs, tip chicken to pour juices into pan. Remove chicken to platter; cover loosely with foil. Let rest for 20 minutes before carving.
Gravy: Meanwhile, tilt pan so juices collect at 1 end. Skim fat from surface, reserving 1 tbsp. In small bowl, stir together butter, flour and reserved fat; set aside. Place pan over medium heat; whisk in wine. Cook, whisking and scraping up browned bits, until reduced by half, about 1 minute.