Merge "Treat two TaskFragment leashes as one for TASK_FRAGMENT_OPEN/CLOSE" into sc-v2-dev am: df04e22915 am: 29c5ed6252

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/15959427

Change-Id: Ic1084e87f8bea90dcf93d71ed81dc48b90304383