Add a switchbar to turn off multi-user feature entirely

Change-Id: Ibf88bf37899af5065c68aeb2337acd4ee48bc13c
Fixes: 72319180
Test: robotest on new controller. Manual test on UserSettings fragment.

src/com/android/settings/users/MultiUserFooterPreferenceController.java

@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2018 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.users;
+
+import android.content.Context;
+
+import com.android.settings.R;
+import com.android.settings.core.BasePreferenceController;
+import com.android.settingslib.widget.FooterPreference;
+import com.android.settingslib.widget.FooterPreferenceMixin;
+
+import androidx.annotation.VisibleForTesting;
+import androidx.preference.Preference;
+
+public class MultiUserFooterPreferenceController extends BasePreferenceController {
+
+    @VisibleForTesting
+    final UserCapabilities mUserCaps;
+
+    private FooterPreferenceMixin mFooterMixin;
+
+    public MultiUserFooterPreferenceController(Context context) {
+        super(context, "dummy_key");
+        mUserCaps = UserCapabilities.create(context);
+    }
+
+    public MultiUserFooterPreferenceController setFooterMixin(FooterPreferenceMixin footerMixin) {
+        mFooterMixin = footerMixin;
+        return this;
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return (mUserCaps.mEnabled && !mUserCaps.mUserSwitcherEnabled)
+                ? AVAILABLE_UNSEARCHABLE
+                : DISABLED_FOR_USER;
+    }
+
+    @Override
+    public void updateState(Preference preference) {
+        mUserCaps.updateAddUserCapabilities(mContext);
+        final FooterPreference pref = mFooterMixin.createFooterPreference();
+        pref.setTitle(R.string.user_settings_footer_text);
+        pref.setVisible(isAvailable());
+    }
+}