Add IDL and stub implementation for chrome.usersPrivate API.

chrome/common/extensions/api/users_private.idl

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Use the <code>chrome.usersPrivate</code> API to manage users.
+namespace usersPrivate {
+
+  callback UsersCallback = void (DOMString[] emails);
+  callback UserAddedCallback = void (boolean success);
+  callback IsOwnerCallback = void (boolean isOwner);
+  callback ManagedCallback = void (boolean managed);
+
+  interface Functions {
+    // Gets a list of the canonicalized emails of the currently whitelisted
+    // users.
+    static void getWhitelistedUsers(UsersCallback callback);
+
+    // Adds a new user with the given email to the whitelist.
+    // The callback is called with true if the user was added succesfully, or
+    // with false if not (e.g. because the user was already present).
+    static void addWhitelistedUser(DOMString email, UserAddedCallback callback);
+
+    // Removes the user with the given email from the whitelist.
+    static void removeWhitelistedUser(DOMString email);
+
+    // Whether the current user is the owner of the device.
+    static void isCurrentUserOwner(IsOwnerCallback callback);
+
+    // Whether the whitelist is managed by enterprise.
+    static void isWhitelistManaged(ManagedCallback callback);
+  };
+};