[automerger] [DO NOT MERGE] Update Platform Security String to 2019-03-01 for nyc-dev Bug:122541777 am: 7a403979d6 am: e56e5efec9 am: 87877d530a am: 33ecfffc1f

Change-Id: I4268b17fbd7e064dd5c1a77048ef238ce2eb3075