Merge "Add OWNERS for back navigation files in WMShell." into tm-qpr-dev am: 5b1020a99d

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20425870

Change-Id: I28a03e302bb0aee7c8de699355222bb0a73a1a53
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>