Saudi Arabia plans to host a Chinese-Arab summit on December 9 attended by Chinese President Xi Jinping during his visit to the kingdom, three Arab diplomats in the region familiar with the plans said on Wednesday. Xi is scheduled to arrive in Riyadh on December 7, two of the diplomats and a fourth source with direct knowledge of the visit said, on a trip that comes at a sensitive time for Saudi-U.S. relations that have been strained by a dispute over energy supplies and concerns over growing Chinese influence in the Middle East. Invitations have gone out to leaders in the Middle East and Nort…