Create BatterySaverReceiver

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

tests/robotests/src/com/android/settings/fuelgauge/BatterySaverControllerTest.java

@@ -17,10 +17,12 @@ package com.android.settings.fuelgauge;
 
 import android.content.Context;
 import android.os.PowerManager;
+
 import com.android.settings.testutils.SettingsRobolectricTestRunner;
 import com.android.settings.TestConfig;
 import com.android.settings.widget.MasterSwitchPreference;
 import com.android.settingslib.core.lifecycle.Lifecycle;
+
 import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -77,6 +79,20 @@ public class BatterySaverControllerTest {
         testUpdateStateInner(false);
     }
 
+    @Test
+    public void testOnBatteryChanged_pluggedIn_setDisable() {
+        mBatterySaverController.onBatteryChanged(true /* pluggedIn */);
+
+        verify(mBatterySaverPref).setSwitchEnabled(false);
+    }
+
+    @Test
+    public void testOnBatteryChanged_notPluggedIn_setEnable() {
+        mBatterySaverController.onBatteryChanged(false /* pluggedIn */);
+
+        verify(mBatterySaverPref).setSwitchEnabled(true);
+    }
+
     private void testOnPreferenceChangeInner(final boolean saverOn) {
         when(mPowerManager.setPowerSaveMode(saverOn)).thenReturn(true);
         when(mPowerManager.isPowerSaveMode()).thenReturn(!saverOn);