Cherry-picked from oc-dev
This cl elicits BatterySaverReceiver that listen to the change about
battery state and battery saver state.
BatterySaverController and BatterySaverSettings will use this receiver
to update the UI.
Bug: 32410757
Test: RunSettingsRoboTests
Change-Id: Ia92c6776985b89fe6a8d5b8d80898e502942b9b5