Add onion to the pan. Cook, stirring, for 1 minute. Increase heat to high and add wine. Cook, scraping up any browned bits, until the liquid is mostly evaporated, about 2 minutes. Reduce heat to medium and stir in cream, any accumulated juices from the chicken and the remaining 1/8 teaspoon each salt and pepper; simmer for 2 minutes. Stir in pesto and tomatoes, then return the chicken to the pan. Turn to coat; cook until warmed through, about 1 minute. Divide the chicken and sauce among 4 plates. Sprinkle with basil.