It has been a good year for pop music on film, from the Brian Wilson biopic, “Love and Mercy,” to the celebration of retro hip-hop, “Dope.” The trend continues with the electric, if slightly hagiographic, “Straight Outta Compton,” a chronicle of the rise of the controversial and groundbreaking California rap group N.W.A. Los Angeles was a jittery, nerve-jangling place in the late 1980s and early 1990s, and not just because of seismic events like the deadly Whittier Narrows and Northridge earthquakes. The fissures between rich and poor, black and white, the police and the policed erupted into deep fault lines, shaking the foundation of the city’s image as a sun-kissed paradise.