Avant garde street performance, politically charged theatre, pro-democracy music and poetry -- powerful works of art dealing with China's bloody Tiananmen Square crackdown that were once commonplace in Hong Kong have all but disappeared in recent years. For decades, tens of thousands of people gathered annually in Hong Kong's Victoria Park for a candlelight vigil marking June 4, 1989, when Chinese troops moved into Beijing's Tiananmen Square to quell peaceful protests calling for reforms. Hundreds, by some estimates more than 1,000, were killed in the crackdown. Any mention of the day -- let alone commemoration -- has long been forbidden...