Preheat oven to 450f.pour oil into large roasting pan.Add chicken;onion;and mushrooms;turning to coat with oil.bake 5 mins;turn chicken over and stir vegetables.bake an additional 5 min.
Meanwhile;in medium bowl;whisk flour into chicken broth. Add vinegar;lemon juice;salt and pepper;stirring well.
When chicken has cooked for 10 min;add broth mixture to roasting pan; cover with foil and bake 10 min,Remove foil;stir begetables and bake,uncovered,until sauce bubbles and is slighty thickened, about 10 min.
heat broiler Turn chicken over,place pan 6 inches from heat and broil unto chicken just stars to turn golden,about 3 or 5 min. Serve immmediately