The carjacker forced his way into her Lexus, sideswiped a police cruiser and led officers on a chase that reached speeds of more than 100 mph Wednesday night, police said. The woman, who was in the car with her 20-month-old son, had a harrowing, split-second decision to make. As the car rounded the outer loop of the Beltway in Bethesda, police said she clutched the toddler to her chest and dived out of the car. “The front door opened and she rolled out,” said Elena Russo, a spokeswoman for the Maryland State Police.