Merge "Invalidate empty pages at the start of wallpaper" into tm-dev am: 16d26136

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/17756831



Change-Id: Id556d21c27e0435d504b1a748b40673f4facacb7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>