Make BatteryDatabaseManager singleton

In BatteryTipLoader, two threads may access BatteryDatabaseManager
simultaneously. In this case thread A may close the database thread B
holds, then settings will crash.

In this cl, we make the BatteryDatabaseManager as singleton and
synchronize all the database related method. Then it shouldn't have
the crash anymore.

Bug: 73346734
Test: RunSettingsRoboTests
Change-Id: Ib53b2894b25155cca0c6ec60d1a816663d27a578

tests/robotests/src/com/android/settings/testutils/DatabaseTestUtils.java

@@ -19,6 +19,7 @@ package com.android.settings.testutils;
 import android.content.Context;
 
 import com.android.settings.fuelgauge.batterytip.AnomalyDatabaseHelper;
+import com.android.settings.fuelgauge.batterytip.BatteryDatabaseManager;
 import com.android.settings.search.IndexDatabaseHelper;
 import com.android.settings.slices.SlicesDatabaseHelper;
 
@@ -30,6 +31,7 @@ public class DatabaseTestUtils {
         clearSearchDb(context);
         clearSlicesDb(context);
         clearAnomalyDb(context);
+        clearAnomalyDbManager();
     }
 
     private static void clearSlicesDb(Context context) {
@@ -76,4 +78,16 @@ public class DatabaseTestUtils {
             throw new RuntimeException();
         }
     }
+
+    private static void clearAnomalyDbManager() {
+        Field instance;
+        Class clazz = BatteryDatabaseManager.class;
+        try {
+            instance = clazz.getDeclaredField("sSingleton");
+            instance.setAccessible(true);
+            instance.set(null, null);
+        } catch (Exception e) {
+            throw new RuntimeException();
+        }
+    }
 }