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: 19b75a48

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



Change-Id: Ibf73e36ae817e815851363814a93e45bb33c12bd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>