Merge "Turn off rounded corners for letterbox by default." into sc-v2-dev am: 92d14a2afd am: e75f02852e

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16297154

Change-Id: Ib8dd50681de46d9cca37c4d6a14eede3d07bb987