Having ground and vcc swapped is very different than just shorting ground and vcc. USB protects against overcurrent and transients, but if you are applying something above 5V or below 0V to any of the USB pins, all bets are off. Since the chromebook was ungrounded, 5V became ground. This means that from the laptops perspective, -5V was applied to the VCC pin. that's 10V out of spec.