Dropbox Inc has secured $250 million from Blackrock Inc and other investors in a new funding round that values the provider of online storage services at almost $10 billion, according to two people familiar with the matter. The sources declined to be named because the funding round was private. Dropbox, the 6-year-old Silicon Valley startup many expect to go public sometime this year, is taking advantage of flush investors and skyrocketing valuations for fledgling tech companies. Other companies, including Microsoft Corp and Amazon Inc are expanding into the cloud business.