Choose your battles. My friend says "You don't have to go to every fight you're invited to." So decide if you can be flexible about the chair, but then be extremely firm about the throwing. If he's not hungry, he can tell you with words or some sign/signal. The food gets put away, not thrown. He will not starve at this age. Offer a variety of foods from which he can choose - if he refuses something on his plate, fine, but he can't throw it. Take it away and excuse him from the chair or table. In 20 minutes when he tells you he's hungry, he goes back to the table and the same food is put out. Try not to react or buy into his tantrum - and I know that's so hard when you just want to blow up! He should not get attention, even negative attention, when he behaves badly.
It's normal for kids to assert their independence especially in areas where they have complete control! That includes eating, sleeping and eventually toilet training. You can't force any of these activities. However, you CAN control your own reaction and your own rules.
Good luck!