Merge "Set default title for PreviewFragment" into ub-launcher3-master am: 2fb840b539 am: c97d495df9

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/12068922

Change-Id: I1d4aaef5d7b6525ec1506636b65cfdcc274ac69d