Merge "Updates documentation on Action Button Icons" into tm-dev am: 3d790a16

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/17928040



Change-Id: Ie1f3bae20d4313e8f8b3481bce59e77f61c65f54
Ignore-AOSP-First: this is an automerge
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>