Move battery stats loading to AsyncLoader.

It takes 3-4 seconds to load the battery settings page in Ryu. Main
reason is that it takes too long to init BatteryStatsHelper.

This cl moves loading code to AsyncLoader, and we will refresh ui once
the loading part is finished.

Following cl will add animation for the battery header to make it not
so janky

Bug: 37196170
Test: RunSettingsRoboTest
Change-Id: I40dfdde4a072e28a56c8fdf0ec6d671b5109fc6d

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

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2017 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 static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.verify;
+
+import android.content.Context;
+import android.os.BatteryStats;
+import android.os.Bundle;
+import android.os.UserManager;
+
+import com.android.internal.os.BatteryStatsHelper;
+import com.android.settings.SettingsRobolectricTestRunner;
+import com.android.settings.TestConfig;
+
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+import org.robolectric.annotation.Config;
+
+@RunWith(SettingsRobolectricTestRunner.class)
+@Config(manifest = TestConfig.MANIFEST_PATH, sdk = TestConfig.SDK_VERSION)
+public class BatteryStatsHelperLoaderTest {
+    @Mock
+    private BatteryStatsHelper mBatteryStatsHelper;
+    @Mock
+    private Bundle mBundle;
+    @Mock
+    private Context mContext;
+    @Mock
+    private UserManager mUserManager;
+    private BatteryStatsHelperLoader mLoader;
+
+    @Before
+    public void setUp() {
+        MockitoAnnotations.initMocks(this);
+
+        mLoader = new BatteryStatsHelperLoader(mContext, mBundle);
+        mLoader.mUserManager = mUserManager;
+    }
+
+    @Test
+    public void testInitBatteryStatsHelper_init() {
+        mLoader.initBatteryStatsHelper(mBatteryStatsHelper);
+
+        verify(mBatteryStatsHelper).create(mBundle);
+        verify(mBatteryStatsHelper).refreshStats(BatteryStats.STATS_SINCE_CHARGED,
+                mUserManager.getUserProfiles());
+    }
+}