I don't think Dropbox ever lost that much per year. $200M was lost in 2016 (once Dropbox decided to not burn money like crazy); $300M in 2015. Source: S1 (https://www.sec.gov/Archives/edgar/data/1467623/000119312518...). In general losses were shrinking, not growing.
(Don't believe the 2018 annual numbers; something like $450M of that "loss" is the result of accounting issues where RSUs converting to stock at IPO is considered an expense)
(Don't believe the 2018 annual numbers; something like $450M of that "loss" is the result of accounting issues where RSUs converting to stock at IPO is considered an expense)