[automerger skipped] [DO NOT MERGE] Update Security String to 2018-04-01 Bug: 73240847 skipped: 5b07fbe498 skipped: ab40f0170c skipped: df3319a7fb skipped: ccd891285c skipped: dd276ca966 skipped: 8501efda49

Change-Id: Ia1823874bf668652495bdde1f9142ef50f0519fd