Each and everytime when you get new Latitude and Longitude, just call one user defined method, like, drawTrack(). But before that whatever value you got first time, just store that value in like in previous_lat and previous_long variable. Then, when you got lat-long second time that means your source lat-long is previous_lat and previous_long and latest one is which you have got currently. Then give that 4 vaues to drawTrack() method.
Inside DrawTrack() method,
googleMap.addPolyline(new PolylineOptions().add(new LatLng(Double.parseDouble(YOUR PREVIOUS LATITUDE VALUE), Double.parseDouble(YOUR PREVIOUS LONGITUDE VALUE), new LatLng(Double.parseDouble(YOUR LATEST LATITUDE VALUE), Double.parseDouble(YOUR LATEST LONGITUDE VALUE).width(5)     .color(getResources().getColor(R.color.BLACK)).geodesic(true));