My 15 month-old does the same thing, in fact he tosses his food on the floor, then looks at me, wags his finger and says "no, no." I started showing him months ago that I wanted his food to stay on his tray or in his mouth. I would tap his tray and then touch his lips as I said this to show him. Now he also throws the food then points to his tray and touches his lips. Kids! :)
Anyway, when he throws food now, mealtime is over. Anything else just seems to be a game for him, but this does seem to work, if for no other reason than he has nothing to throw. When he starts throwing food, I take his tray, get him out of the chair, wash him up and we move on to something else. If he's hungry again later, I offer whatever is left that he didn't chuck onto the floor.
Good luck!