[automerger skipped] [RESTRICT AUTOMERGE] Add hide-non-system-overlay flag for HarmfulAppWarningActivity am: 53ee9c24 am: be7090b0 -s ours

am skip reason: subject contains skip directive

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16743244

Change-Id: I6d20a426e2f84a3bb4ef16999924024ba93e4e21