WASHINGTON — The Supreme Court’s decision could come Friday in the case about whether TikTok must shut down in a few days under a federal law that seeks to force its sale by the Chinese company that owns the social media platform used by 170 million people in the U.S. The justices are weighing a free speech challenge to the law, which takes effect Sunday, against the national security concerns that prompted its enactment with broad bipartisan support last year.