[DO NOT MERGE] Enforce user separation on external storage am: 5432cedb61 am: c3c4b15dee am: 7d869bd17f am: 0312164f4b  -s ours am: 45beb672fd am: aab2da8ce2 am: 7feb74def7 am: 85e9579545 am: 8d7de50654
am: 27461551e9  -s ours

Change-Id: I1f420f1b2272485698c56289bba34c9e5dea4dbc