Indra Nooyi became C.E.O. of PepsiCo just in time for a global financial meltdown. She also had a portfolio full of junk food just as the world decided that junk food is borderline toxic. Here&`&s the story of how she overhauled that portfolio, stared down activist investors, and learned to "leave the crown in the garage." (Part 3 of a special series, "The Secret Life of C.E.O."s ”)