Place the mushrooms, onion, 1 c. chicken broth, red wine, tomato paste, garlic, rosemary, thyme, bay leaf and pepper in a slow cooker. Stir, making sure that the tomato paste has been incorporated.
Add the chicken thighs. Replace the cover on the slow cooker. Set the slow cooker on low heat and cook for 7 - 8 hours or set it on high heat and cook for 3 1/2 - 4 hours.
At the end of the cooking time, remove the chicken and vegetables to a plate, cover and keep warm. Skim the fat from the pan sauce. Measure the remaining sauce. Add more chicken broth if necessary to make 2 c.
Transfer the liquid to a medium sauce pan. Combine 1/4 c. chicken broth with flour in a small bowl. Stir until smooth.
Add the flour broth mixture to the sauce pan. Cook the sauce on medium heat until thick and bubbling.
Drizzle some of the sauce over the chicken. Put the remaining sauce into a gravy boat to pass around. Sprinkle the parsley over the chicken and serve.