More than a decade ago in Los Angeles, hundreds of people protested in the streets after police killed a man in a controversial shooting. The crowd rolled dumpsters down a hill into police cars, threw air conditioners out of windows, hurled rocks and bottles at officers. As he responded from a neighboring district to help, Blake Chow, then a commander with the Los Angeles Police Department, spotted Todd Chamberlain, a LAPD captain, also arriving on scene, and felt a wave of relief. “When I got there and saw Todd, I knew we were going to get control of it and calm everything down,” Chow, now an assistant chief with the LAPD, said in an interview last week.