With concerts by Jay-Z and Bruce Springsteen scheduled for 1st Mariner Arena, the second half of 2009 is already shaping up to be a big year for live music in Baltimore. But what if we also got U2? As it turns out, we almost did. Here's Sun writer Kevin Van Valkenburg with details: I asked Ravens president Dick Cass about potentially booking more non-sporting events at M&T Bank Stadium as a potential revenue source, since I remembered that they had Kenny Chesney play there. Cass said that the Ravens were negotiating with promoters about a potential U2 concert this fall, was interested in doing it until the date U2 offered conflicted with the Ravens schedule. ...