Cook bacon in a large skillet over medium heat until just crisp. Remove from skillet to a paper towel-lined plate. Set aside. Discard all but 2 tablespoons of fat from the skillet.
Season both sides of chicken with salt and pepper. Brown the chicken, turning once, about 3-4 minutes per side. Transfer to a large plate.
Add butter and mushrooms to skillet and cook until mushrooms begin to brown, about 5 minutes. Add onions, carrots, garlic, salt and pepper and cook until vegetables begin to soften, about 8 minutes.
Transfer vegetable mixture to slow cooker. Add chicken broth. Place chicken and any juices from plate and bacon on top of vegetables. Add wine, thyme sprigs and pearl onions. Cover and cook on low for 5 and a half hours.
For a thicker sauce, mix 1-2 tablespoons cornstarch with 1-2 tablespoons of water until smooth and no lumps appear. I like to remove the chicken from the slow cooker to a plate before mixing in the cornstarch mixture. (If you like the sauce thicker you can add another tablespoon cornstarch mixed with another tablespoon water). Add the chicken back to the slow cooker and continue to cook for 1 hour on high.
Season with salt and pepper, and serve immediately. I like to serve mine with mashed potatoes.