WASHINGTON — The Justice Department announced Tuesday that it would not bring federal criminal charges against two Cleveland police officers in the 2014 killing of 12-year-old Tamir Rice, saying video of the shooting was of too poor a quality for prosecutors to conclusively establish what had happened.In closing the case, the department brought to an end a long-running investigation into a high-profile shooting that helped galvanize the Black Lives Matter movement and that became part of the national dialogue about police …