Merge "Explicitly mention a confusing proto3 infelicity." into main am: 3a0c095253

Original change: https://android-review.googlesource.com/c/platform/system/core/+/3531073

Change-Id: I4a7e26650f5708129a8d846fe9e9618c61a0d9e2
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>