Last month, midway through a whirlwind tour of United States universities, Hong Kong democracy activist Joshua Wong took a break for a crab cake and mac-and-cheese lunch at a Manhattan brasserie. Wong, 19, came to international prominence during the Umbrella Movement of 2014 as the face and voice of a generation of Hong Kong youngsters dissatisfied with politics in a Chinese city that was once a British colony. By then, Wong was already something of a veteran agitator.