Begin transition from BatteryStatsHelper to BatteryUsageStats API.

For now, keep both BatteryStatsHelper and BatteryUsageStats in play.
The plan is to transition from the former to the latter, one usage
at a time.  When all is said and done, all references to
BatteryStatsHelper will be gone.

Bug: 173745486
Test: atest --host SettingsRoboTests

Change-Id: I37e1dfff0043b1845992f18d72067bb547bb69ff

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

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.fuelgauge;
+
+import android.content.Context;
+import android.os.BatteryStatsManager;
+import android.os.BatteryUsageStats;
+
+import com.android.settingslib.utils.AsyncLoaderCompat;
+
+/**
+ * Loader to get new {@link BatteryUsageStats} in the background
+ */
+public class BatteryUsageStatsLoader extends AsyncLoaderCompat<BatteryUsageStats> {
+    private final BatteryStatsManager mBatteryStatsManager;
+
+    public BatteryUsageStatsLoader(Context context) {
+        super(context);
+        mBatteryStatsManager = context.getSystemService(BatteryStatsManager.class);
+    }
+
+    @Override
+    public BatteryUsageStats loadInBackground() {
+        return mBatteryStatsManager.getBatteryUsageStats();
+    }
+
+    @Override
+    protected void onDiscardResult(BatteryUsageStats result) {
+    }
+}