Merge "[7/n] Pin ActivityStack" into udc-qpr-dev am: 0926aa9033 am: 33643ec4b8

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/24368154

Change-Id: I27a0c9f42493f04f2488d68df1758625980fe545
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>