Merge "Factor our mChildrenChanged from doTransaction" into sc-dev am: 0aa188a3 am: 2db0765a am: 4f20aaa6

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/14949463

Change-Id: Ib73691feab51c3a9587fd39c8d9a7b9b3a7e1b29