It could be those tiny slugs, but it looks very similar to a bug that often invades my garden tomatoes....the "potato flea beetle" is what it's known as. Look for tiny, flea-like beetles that jump. You have to catch them at the right time of day or they retreat to the surrounding soil. They jump from the soil, chew for awhile and then jump off. My guess is that you have something similar. Grasshoppers tend to chew the edges of the leaves.
If it was slugs, then you'd see slime somewhere.
-2cents