Implement alternate power button behavior for dreams. am: bffe18bf28

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/20132039

Change-Id: I906067a2d0763943e95f57149543eb59146f83e1
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>