Add battery percentage switch to display settings

Test: mmma packages/apps/Settings/tests/robotests
Bug:32539932
Change-Id: I08c1d0f3b6cb8be7d1456268498356f7ed833e5c

src/com/android/settings/display/BatteryPercentagePreferenceController.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright (C) 2016 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.display;
+
+import android.content.Context;
+import android.provider.Settings;
+import android.support.v7.preference.Preference;
+import android.support.v14.preference.SwitchPreference;
+
+import com.android.settings.core.PreferenceController;
+
+import static android.provider.Settings.System.SHOW_BATTERY_PERCENT;
+
+/**
+ * A controller to manage the switch for showing battery percentage in the status bar.
+ */
+
+public class BatteryPercentagePreferenceController extends PreferenceController
+        implements Preference.OnPreferenceChangeListener {
+
+    private static final String KEY_BATTERY_PERCENTAGE = "battery_percentage";
+
+    public BatteryPercentagePreferenceController(Context context) {
+        super(context);
+    }
+
+    @Override
+    public boolean isAvailable() {
+        return true;
+    }
+
+    @Override
+    public String getPreferenceKey() {
+        return KEY_BATTERY_PERCENTAGE;
+    }
+
+    @Override
+    public void updateState(Preference preference) {
+        int setting = Settings.System.getInt(mContext.getContentResolver(),
+                SHOW_BATTERY_PERCENT, 0);
+
+        ((SwitchPreference) preference).setChecked(setting == 1);
+    }
+
+    @Override
+    public boolean onPreferenceChange(Preference preference, Object newValue) {
+        boolean showPercentage = (Boolean) newValue;
+        Settings.System.putInt(mContext.getContentResolver(), SHOW_BATTERY_PERCENT,
+                showPercentage ? 1 : 0);
+        return true;
+    }
+}