[automerger skipped] [RESTRICT AUTOMERGE] Add hide-non-system-overlay flag for HarmfulAppWarningActivity am: f36b7b9f am: aa0349bc -s ours

am skip reason: subject contains skip directive

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16742068

Change-Id: I9b56ef5961c49e4142ffcf870a43d1149683c767