Well, I think that if Black accepts the gambit white gets a slight advantage. 

1. e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Bxc6 dxc6 5.0–0 f6 6.d4 Bg4 7.c3 exd4 8.cxd4 Qd7 9.h3 Bxf3 10.Qxf3 Qxd4 11.Rd1 

11...Qc4 This is best. 12.Bf4 Qf7 (12...Qe6 13.Bxc7 Nh6 14.Qe3±) 13.Qg3 f5 (13...Rc8 14.Qg4 Rd8 15.Rxd8+ Kxd8±) 14.exf5 Be7 (14...Ne7 15.Qe3 Qxf5 16.Bxc7 g6 17.Bd6 Rd8 18.Nc3 Kf7 19.g4+-) 15.Nc3 Nf6 16.Bxc7 0–0 17.a3 White has a slight advantage

11 ... Qe5? 12.Bf4 Qe7 [12...Qxb2 13.Nc3 White has a significant advantage. ] 13.Nc3 Qf7 [13...g5 14.Qh5+ Qf7 15.Qxf7+ Kxf7 16.Bxc7 White's way ahead; 13...Nh6 14.Bxh6 gxh6 15.Qh5+ Qf7 16.Qxf7+ Kxf7 17.Rd7+±] 14.a3 This isn't the only move to gain an advantage. [14.Qg3!?; 14.Rd2!?] 14...Bc5! White gains an advantage against all other moves as well. 15.b4 Ba7 [15...Bb6 16.Qd3 Qe6 17.Qg3 Qf7 18.Na4 Ne7 19.Bxc7±] 16.Rac1 White gains a significant advantage in every variation 16...g5 [16...Rd8 17.Rxd8+ Kxd8 18.Be3 Bxe3 (18...c5 19.Rd1+ Ke8 (19...Kc8 20.Qf5+ White wins) 20.Qf5 White Wins) 19.Qxe3 White wins; 16...f5 17.exf5 Ne7 18.Qe2 Qxf5 19.Bxc7±] 17.Bh2 h5 18.Nd5 g4 [18...cxd5? 19.Rxc7+-] 19.Qd3 Bb6 20.Nxb6 cxb6 21.Rc4+-