No one! It was a rhetorical question…
Nothing says it was a gift; (the grammar of Eph 2:8-9 has been irreducibly shown to demonstrate this) and it is only given as a part of the Imago Dei. The ability to trust, believe, have faith in something or someone is as much a part of human nature as the ability to breathe.
We cannot believe, however, if nothing is presented as being believable. We cannot enter into a relationship unless the other person is willing. The gospel is God saying he is willing, in spite of ourselves, and only asks us to trust in his willingness above all others in whom we have trusted.
But faith precedes the new heart, for it is through, by means of our faith that God extends his graciousness to give us a new heart. The result of his graciousness is, in part, his Spirit indwelling us, which causes us to be capable of being obedient to the Lord.
Doug