Fans of pop star Katy Perry woke up Friday to an e-mail on their smartphones: Her new single, “Chained to the Rhythm,” is available for streaming. They got another reminder when they logged on to Facebook, where Perry is liked by more than 70 million people. As if that weren’t enough, Los Angeles and London fans on their daily commutes were greeted by billboards. The best part for Perry? It’s all free. Spotify Ltd., the world’s most popular paid music service, will run a months-long pr