In a 3-1/2- or 4-quart slow cooker place mushrooms and onions. Stir in the 1/2 cup broth, the wine, tomato paste, garlic salt, rosemary, thyme, pepper, and bay leaf. Add chicken.
Cover and cook on low-heat setting for 7 to 8 hours or on high-heat setting for 3-1/2 to 4 hours. Transfer chicken to a serving platter; keep warm.
For sauce, transfer vegetables and cooking liquid to a medium saucepan. Combine the 1/4 cup broth and the flour; stir into mixture in saucepan. Cook and stir until thickened and bubbly; cook and stir 1 minute more. Discard bay leaf. Spoon some of the sauce over chicken; pass remaining sauce. If desired, sprinkle with parsley. Makes 4 servings.