Merge "Updates documentation on Action Button Icons" into tm-dev am: 3d790a16 am: 19acfbe9

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



Change-Id: Ie86a984f791d22d94a25fe7e0662d5bd06f79004
Ignore-AOSP-First: this is an automerge
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>