CONTRIBUTION, CONVEYANCE AND ASSUMPTION AGREEMENT BY AND AMONG EL PASO PIPELINE PARTNERS, L.P. EL PASO PIPELINE GP COMPANY, L.L.C. EL PASO PIPELINE LP HOLDINGS, L.L.C. EL PASO NORIC INVESTMENTS III, L.L.C. EL PASO CNG COMPANY, L.L.C. El PASO PIPELINE...