Merge "Improve visual debugging for NotificationStackScrollLayout" into sc-v2-dev am: 532102525f am: bd44e93c5c

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16388646

Change-Id: I0a7eb7ad30ad0579f70789cbd3811c8ae20be8ee