San Francisco Mayor Gavin Newsom is considering a 2010 run for governor - a campaign that would embrace many of the same divisive causes he has championed as mayor, including same-sex marriage, universal health care and protections for illegal immigrants, The Chronicle has learned. Newsom has long been rumored to be a potential contender in what is likely to be a crowded field of Democrats looking to succeed Republican Gov. Arnold Schwarzenegger, a list that includes Attorney General and former Gov. Jerry Brown, former state Controller Steve Westly and Los Angeles Mayor Antonio Villaraigosa. In recent months, Newsom has quietly...