Add summary for Backup menu in Settings.

'On'/'Off' depending on whether the backup is enabled in settings.

Refactors BackupSettingsActivity to be shown on System fragment via
xml/PreferenceController instead of category in the manifest.

Bug: 36891827
Test: make RunSettingsRoboTests
Change-Id: I61425fed4d63055c6c386be38792ae074aa72679

src/com/android/settings/backup/BackupSettingsActivityPreferenceController.java

@@ -0,0 +1,64 @@
+/*
+ * 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.backup;
+
+import android.app.backup.BackupManager;
+import android.content.Context;
+import android.os.Build;
+import android.os.RemoteException;
+import android.os.ServiceManager;
+import android.os.UserManager;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.PreferenceScreen;
+import android.util.Log;
+
+import com.android.settings.R;
+import com.android.settings.Utils;
+import com.android.settings.core.PreferenceController;
+
+public class BackupSettingsActivityPreferenceController extends PreferenceController {
+    private static final String KEY_BACKUP_SETTINGS = "backup_settings";
+    private static final String TAG = "BackupSettingActivityPC" ;
+
+    private final UserManager mUm;
+    private final BackupManager mBackupManager;
+
+    public BackupSettingsActivityPreferenceController(Context context) {
+        super(context);
+        mUm = (UserManager) context.getSystemService(Context.USER_SERVICE);
+        mBackupManager = new BackupManager(context);
+    }
+
+    @Override
+    public boolean isAvailable() {
+        return mUm.isAdminUser();
+    }
+
+    @Override
+    public String getPreferenceKey() {
+        return KEY_BACKUP_SETTINGS;
+    }
+
+    @Override
+    public void updateState(Preference preference) {
+        final boolean backupEnabled = mBackupManager.isBackupEnabled();
+
+        preference.setSummary(backupEnabled
+                ? R.string.accessibility_feature_state_on
+                : R.string.accessibility_feature_state_off);
+    }
+}