Merge "Set alpha to 0 on attach to avoid flicker at transition start." into...

Merge "Set alpha to 0 on attach to avoid flicker at transition start." into udc-dev am: dc472531 am: bdb153f5 am: 29001875

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/23252176



Change-Id: I488e27d6b91e97430013116f1bbbcde63b5519a4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>