This study is conducted to explore a new therapy for anemia in patients with chronic kidney disease. Anemia is a reduced number of red blood cells or hemoglobin. Hemoglobin (which contains iron) is important for the transport of oxygen in your blood. The purpose of the study is to see if Roxadustat is effective and safe to treat anemia in patients with chronic kidney disease. Roxadustat will in this study be compared to darbepoetin alfa, a commercially available medicine for treatment of anemia (tradename Aranesp).