Add animation for battery asyncLoader.

When battery asyncLoader is loading batterystats, show a battery
placeholder(critical level) and animate to real status once data is
loaded.

Bug: 35917699
Test: RunSettingsRoboTests
Change-Id: Ie4ff73ff2cc0b9e17b4541e3284bf2ac34da42c4
Merged-In: Ie4ff73ff2cc0b9e17b4541e3284bf2ac34da42c4