Keep selected time slot and expand state when device is rotate

Bug: 187772493
Test: make SettingsRoboTests
Change-Id: If70abf06825a88f0ad0add37ef8d4f46a0aad1e9

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

@@ -30,6 +30,7 @@ import android.content.Context;
 import android.content.ContentValues;
 import android.content.pm.PackageManager;
 import android.graphics.drawable.Drawable;
+import android.os.Bundle;
 import android.text.format.DateUtils;
 
 import androidx.preference.Preference;
@@ -559,6 +560,27 @@ public final class BatteryChartPreferenceControllerTest {
             .setTimestamps(any());
     }
 
+    @Test
+    public void testOnSaveInstanceState_restoreSelectedIndexAndExpandState() {
+        final int expectedIndex = 1;
+        final boolean isExpanded = true;
+        final Bundle bundle = new Bundle();
+        mBatteryChartPreferenceController.mTrapezoidIndex = expectedIndex;
+        mBatteryChartPreferenceController.mIsExpanded = isExpanded;
+        mBatteryChartPreferenceController.onSaveInstanceState(bundle);
+        // Replaces the original controller with other values.
+        mBatteryChartPreferenceController.mTrapezoidIndex = -1;
+        mBatteryChartPreferenceController.mIsExpanded = false;
+
+        mBatteryChartPreferenceController.onCreate(bundle);
+        mBatteryChartPreferenceController.setBatteryHistoryMap(
+             createBatteryHistoryMap());
+
+        assertThat(mBatteryChartPreferenceController.mTrapezoidIndex)
+            .isEqualTo(expectedIndex);
+        assertThat(mBatteryChartPreferenceController.mIsExpanded).isTrue();
+    }
+
     private static Map<Long, Map<String, BatteryHistEntry>> createBatteryHistoryMap() {
         final Map<Long, Map<String, BatteryHistEntry>> batteryHistoryMap = new HashMap<>();
         for (int index = 0; index < DESIRED_HISTORY_SIZE; index++) {