Make Activites touch opaque - DO NOT MERGE am: 22261fa664

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/18029563

Change-Id: I9f22108994196296b0441681c02357f128bc8947
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>