Salesforce.com Inc. disclosed Monday that it bought 4.9 million shares of Dropbox Inc. during the first quarter, which represents about 1.3% of the shares outstanding. The cloud storage company’s stock went public on March 23, at an initial public offering price of $21, and traded in a range of $27.84 to $34.37 in the five sessions through the end of March. Dropbox’s stock, which rose 0.5% in premarket trade, has inched up 0.1% since the end of March, while Salesforce shares have rallied 12.3% and the S&P 500 has gained 3.3%. Salesforce, the customer relationship management software company, also owned about 888,500 shares of communications software company Twilio Inc. , or about 0.9% of the shares outstanding, and about 45,000 shares of database platform company MongoDB Inc. , or about 0.1% of the shares outstanding, as of March 31. Salesforce’s holdings of Twilio and MongoDB are unchanged since the end of December.