This cl creates BatteryHeaderPreferenceController, which will first
load the battery level in ui thread(in displayPreference()), then
display the remaining time once we get the battery stats.
This is the best we can do to avoid ui flashing while removing the
animation
Bug: 38349587
Test: RunSettingsRoboTests
Merged-In: Ic3622bb73562ba42e69b37e5674a724c03c45f12
Change-Id: Ic3622bb73562ba42e69b37e5674a724c03c45f12
