Add trial to bracket assuming bracket is not filled.

        At a later iteration, a newly added trial will be given equal
        opportunity to catch up.

def add_trial(self, trial):
        """Add trial to bracket assuming bracket is not filled.

        At a later iteration, a newly added trial will be given equal
        opportunity to catch up."""
        assert not self.filled(), "Cannot add trial to filled bracket!"
        self._live_trials[trial] = None
        self._all_trials.append(trial)