Stone tools predate even the oldest suggestions of intentional fire use by at least a million years, so the cooking hypothesis isn't particularly compelling. Elsewhere in this thread I've also discussed how it's not really an explanation either.
The cooking hypothesis is not well known, however, from what I understand, this was when we went from having big guts and average brains to small guts and big brains. The fossil record of primates is far from complete, but roughly speaking, we have been eating cooked food for a million years.
The stone tools that predate this by a few million years reinforce the cooked food hypothesis in this 'chicken or egg' situation.