PALO ALTO — Denise Herrmann was only a few months into her new job as principal of a Palo Alto high school in fall 2014 when a student took his own life.By the next day, Herrmann said, she and some of her colleagues at Henry M. Gunn High School were in conversations with experts from nearby Stanford University about how to cope with student suicides and their aftermath.She knew her school was not alone.