LONDON — Documents leaked by former NSA contractor Edward Snowden suggest that spy agencies have a powerful ally in Angry Birds and a host of other apps installed on smartphones across the globe.The documents, published Monday by The New York Times, the Guardian, and ProPublica, suggest that the mapping, gaming and social networking apps that are a common feature of the world's estimated 1 billion smartphones can feed America's National Security Agency and Britain's GCHQ with huge amounts of per...