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

src/com/android/settings/fuelgauge/BatteryMeterView.java

@@ -38,6 +38,8 @@ public class BatteryMeterView extends ImageView {
     @VisibleForTesting
     ColorFilter mAccentColorFilter;
 
+    private int mLevel;
+
     public BatteryMeterView(Context context) {
         this(context, null, 0);
     }
@@ -64,6 +66,7 @@ public class BatteryMeterView extends ImageView {
     }
 
     public void setBatteryLevel(int level) {
+        mLevel = level;
         mDrawable.setBatteryLevel(level);
         if (level < mDrawable.getCriticalLevel()) {
             mDrawable.setBatteryColorFilter(mErrorColorFilter);
@@ -72,6 +75,10 @@ public class BatteryMeterView extends ImageView {
         }
     }
 
+    public int getBatteryLevel() {
+        return mLevel;
+    }
+
     public void setCharging(boolean charging) {
         mDrawable.setCharging(charging);
     }