Add support for visualizing secondary users.

This functionality adds the secondary users to the screen, but
currently does not populate the information for them. Once the
external stats query works, I will add a loader which will
populate this information.

This also does not cover work profiles. Support for that is
forthcoming.

Bug: 34715777, 34225103
Test: Settings Robotest
Change-Id: Ib9b692b214f5ce5d303dfd64516381443d4acebd

src/com/android/settings/applications/UserManagerWrapper.java

@@ -0,0 +1,32 @@
+/*
+ * 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.applications;
+
+import android.content.pm.UserInfo;
+
+import java.util.List;
+
+/**
+ * This interface replicates a subset of the android.os.UserManager. The interface
+ * exists so that we can use a thin wrapper around the UserManager in production code and a mock in
+ * tests. We cannot directly mock or shadow the UserManager, because some of the methods we rely on
+ * are newer than the API version supported by Robolectric or are hidden.
+ */
+public interface UserManagerWrapper {
+    UserInfo getPrimaryUser();
+    List<UserInfo> getUsers();
+}