“The coming film, which recounts a violent 1831 slave rebellion and includes scenes that evoke present-day outrage over fatal police shootings of black men, has been marketed as an urgent call to action. … But when The Birth of a Nation arrives in roughly 2,000 theaters on Friday, Fox Searchlight is hoping that a parallel and largely invisible marketing effort – one intended to contain and frame Mr. Parker’s message – will ease the film into communities already on edge.”