Merge "Updates documentation on Action Button Icons" into tm-dev am: 3d790a16 am: 2b5a19e8 am: c4616a52

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



Change-Id: Ia9a0774f9b02b7d74f3633d44897be39b683d4cf
Ignore-AOSP-First: this is an automerge
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>