Drop supplementary groups for child zygotes. am: 7c8779c0 am: 80cfa981 am:...

Drop supplementary groups for child zygotes. am: 7c8779c0 am: 80cfa981 am: 75f35b04 am: 89a122db am: f537d354

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/11691614

Change-Id: I636c74e4b1723abaf70764c2258462f7b5ee2945