[sf] make legacy frontend debug flag persistent am: 3e76a50f

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/21801174



Change-Id: I8eca22713762ed0a9bcb3aa63778e39e2dc8e0c5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>