When Mary Ann Prince first heard of supervised injection sites, where intravenous drug users can inject — under medical supervision — she was skeptical at best.“I thought it just continues this (addiction) for the kid,” the Shirley woman said.It took just one thing to change her mind: On May 2, 2014, her son, Travis, a National Guard Army reservist who became addicted to prescription painkillers after a back injury and then turned to heroin, died of an overdose.He was 25 and left behind a wife and 9-month-old son.