Merge "Return the existing display ids when registering a display window...

Merge "Return the existing display ids when registering a display window listener" into sc-v2-dev am: 31fd5176 am: 064391c9

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15730867

Change-Id: Ia596afdad7a9cf169bce3a07361cda62f6dc1a4f