Exxon Mobil Corp. posted its first quarterly loss in three decades as it and rival Chevron Corp. painted a dismal picture of the oil industry, signaling that the impact of the coronavirus pandemic may hang over their businesses for much of 2020. Exxon swung to a $610 million loss in the quarter as it took a “market-related” $2.9 billion charge. It reported $2.4 billion in profits during the same period last year. The bulk of the impairment was related to its downstream business, which refines oil into gasoline and other products. …