Merge "Make activities in untrusted embedding mode invisible behind overlay"...

Merge "Make activities in untrusted embedding mode invisible behind overlay" into tm-dev am: c0ccf9b0

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16947300

Change-Id: Ibf6f1a2ca6bd3acae24b280f6b105b5486963639