By John Pomfret in The Washington Post Quick: Think of a Chinese brand name. Japan has Sony. Mexico has Corona. Germany has BMW. South Korea? Samsung. And China has . . . ? If you’re stumped, you’re not alone. And for China, that is an enormous problem. Last year, China overtook Germany to become the world’s largest exporter, and this year it could surpass Japan as the world’s No. 2 economy. But as China gains…