Season chicken with salt and pepper. Heat oil. Add chicken pieces to oil and brown all sides. Remove to a plate. Pour off excess fat, reserving about 2 tablespoons. Reduce heat to medium and add onions, bay leaf, rosemary and sage. Cook, stirring constantly until onions are brown. Add garlic. Return chicken to pan and add wine. Boil over medium-high heat until wine is evaporated, turning the chicken and scraping up the brown bits with a wooden spoon. Add tomatoes and chicken stock. Bring to a boil then reduce heat to low. Cover and simmer for 25 minutes. Add mushrooms. Cook, covered for 10 minutes. Uncover and boil the pan juices over high heat until slightly thickened.