Only a few short months ago, JPMorgan Chase traders were on such a roll that they did not have a single losing day in the first quarter. But when the bank reports its second-quarter results this week, that hot streak will have come to an end. Analysts expect JPMorgan to count an almost 20% drop in its sales and trading revenues, reflecting a slowdown in investor activity and the dismal performance of its fixed-income and commodities groups. Bank of America, Citigroup, Goldman Sachs and Morgan Stanley are expected to report similar news.