In small bowl, mix oil and Worcestershire sauce; brush over beef roast. Rub roast evenly with garlic, rosemary, salt and pepper. In 5- to 6-quart slow cooker, add onion. Pour 1/4 cup of the broth over onion. Place beef roast on onion. Refrigerate remaining broth.
Cover and cook on Low heat setting 8 to 9 hours.
Remove beef from cooker; cover to keep warm. In small bowl, mix remaining 3/4 cup broth, the chili sauce and flour; stir into hot mixture in cooker. Increase heat setting to High. Cook uncovered 5 to 10 minutes or until thickened. Serve gravy with beef.