Fast-food giant Yum Brands' once-sizzling growth in China appears to have ground to a halt. The parent of Taco Bell, Pizza Hut and KFC late Thursday said it expects existing-restaurant sales there to slide 4% in the December-ending quarter. It's Yum Brands' (YUM) first same-store sales decline in its largest market in three years. Just a year ago, China comps surged 21%. Yum shares tumbled 6% late on guidance. The stock had risen