Merge "Add test mechanism to check whether the shell drop target window has...

Merge "Add test mechanism to check whether the shell drop target window has drawn" into udc-dev am: d4760a4d am: 73b4f7d1 am: 64acbe36 am: 531457b1

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/22939180



Change-Id: Iabb2378cf6189a35b0b830a4e74d095e4361b684
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>