Exxon Mobil Corp (XOM.N), the world’s largest publicly traded oil company, has changed its U.S. employment policies to prohibit discrimination based on sexual orientation and gender identity as now required by federal law. Investors had pressed for the change for years, filing shareholder proposals for Exxon to guarantee protections against discrimination based on sexual orientation since 1999. Exxon has previously resisted making the change, saying it already prohibited all forms of discrimination at its offices anywhere in the world.