Hollywood has film premières; Silicon Valley has developer conferences. Today Google I/O, the search giant’s annual event, opens in San Francisco. Each year thousands of developers and journalists flock to the two-day show, which drums up enthusiasm for the firm’s line-up of new offerings. The fanfare includes an address from a Google executive, delivered at feature-film length. Among the products Google is expected to show off this year is a photo service, in which pictures can be indexed and searched as easily as e-mails in Gmail. Other areas to watch include virtual reality and the extension of the Android operating system from smartphones to other screens, including TV sets and cars. Google is increasingly becoming a tech conglomerate, working on “moonshot” ideas that could become its next source of growth, as its search-advertising business starts to slow.