Saute onion in butter until golden. Add shrimp and mushrooms and saute until shrimp are pink. Combine salt, pepper, chili sauce and water. Add to shrimp mixture and bring to a boil. Stir in rice, cover and simmer for 5 minutes. Combine sour cream and flour. Add to the shrimp and rice mixture and heat gently (do not bring to a boil). Divide between plates, garnish with chives and parsley and serve.