Jen Friedberg ARLINGTON -- Plastic dolls and heavy breathing took over Cowboys Stadium on Tuesday, as 4,626 people -- most of them Arlington school district eighth-graders -- learned CPR and broke a world record in the process.The session broke the Guinness world record for the largest CPR training session and helped Arlington achieve a goal set by Mayor Robert Cluck in 2005 -- to teach 10 percent of the citys population CPR.The previous record was set in Oslo, Norway, with 3,692 participants.