The Trump administration has begun inserting legal protections into trade agreements to shield online platforms like Facebook, Twitter and YouTube from lawsuits. That move could help lock in America’s tech-friendly regulations around the world even as they are being questioned at home. The legal protections are included in the administration’s two biggest trade deals. One is the United States-Mexico-Canada Agreement; the other is a pact with Japan. American negotiators have proposed including the language in other prospective deals as well.