LONDON — If Steve Hilton succeeds in making it past next week’s gubernatorial primary in California, it will mark a breakthrough by a relative unknown. In the U.K., he is anything but. Hilton, a Republican who played a central role in former British Prime Minister David Cameron’s rise to power, is effectively tied with Democrat Xavier Becerra in the race to be California’s next governor, according to several polls over the last week. Under California’s primary system, the candidates who finish