The SerialDeviceEnumerator class (wrapped in the SerialPortManager Mojo interface) only supports one-off enumerations. In contrast the HID and USB interfaces support registering an observer that is notified when devices are added and removed from the system.

There is already a limited version of this inside SerialIoHandlerWin in order to detect when a USB serial port has been disconnected.

This will enable implementation of the onconnected and ondisconnected event attributes on the Serial object.