Merge "Add java doc for registerVisibleActivityCallback method." into sc-v2-dev am: 786af488fb am: ddfc23c733

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16036450

Change-Id: I24ceeb05c8a47563e208fa0d46c4e60a6ee1c258