https://www.reuters.com/article/usa-senate-facebook/facebook-whistleblower-to-testify-at-u-s-senate-hearing-next-week-lawmakers-say-idUSKBN2GP01T >Two U.S. senators said on Tuesday a Facebook Inc whistleblower will testify at a Senate hearing next week about what one of them called the social media company's "toxic effects" on young users.