Merge "Allow delete empty TaskFragment in PiP" into tm-dev am: d41df35243 am: b52ab7d11e

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/17800404

Change-Id: Ie7b7e0ac95ddf43b10f5a364205230f7d3fc5abe
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>