Cover dried scallops with water and soak overnight or at least 2 hours. Drain and shred into small strings. Reserve soaking liquid. Peel and remove seeds of winter melon. Rinse with water and cut into 1/2-inch chunks. In a 3-quart saucepan, bring the 4 cups chicken stock to boil. Add the winter melon, dried scallop and the soaking liquid, black mushrooms, and sliced ginger. Cover and bring to boil over high heat. Lower heat and let simmer for 5 minutes, or until winter melon is softened. Turn heat back to high, add salt and stir in cornstarch mixture. Add shrimp meat and egg whites. Adjust seasoning. Remove from heat. Serve hot with sprinkles of ground white pepper and chopped cilantro.