[automerger skipped] [DO NOT MERGE] Update Security String to 2018-04-01 Bug: 73240847 skipped: 5b07fbe498 skipped: ab40f0170c skipped: df3319a7fb skipped: ccd891285c skipped: dd276ca966

Change-Id: I946b3f1523f613c3a5e8008ccac78cd7672184ce