Well, you level up the growlithe to level 48 and teach it flare blitz. Then you evolve the growlithe. Then you go to the move rememberer in blackthorn city, trade in a heart scale and teach the arcanine extremespeed.
Another way this can happen is if you breed a female growlithe/arcanine with a male growlithe/arcanine/ponyta/rapidash/combusken/blaziken/monferno/infernape that know flare blitz. This will give the growlithe the move flare blitz when it comes out of the egg. The all you need to do is evolve the growlithe and teach it extremespeed once it levels up to level 39.