arc: Add splash screen for ARC++ Kiosk startup

ui/login/screen_container.css

 /* Copyright 2014 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.
  */
 
 #outer-container {
   -webkit-box-align: center;
   -webkit-box-pack: center;
   -webkit-perspective: 1px; /* Workaround, see http://crbug.com/360567 */
   bottom: 57px;  /* Leave space for the header bar */
@@ skipping 141 matching lines @@
   opacity: 0.4;
   width: 10px;
 }
 
 .progdot-active {
   opacity: 0.5;
 }
 
 #account-picker-dot,
 #app-launch-splash-dot,
+#arc-kiosk-splash-dot,
 #auto-enrollment-check-dot,
 #autolaunch-dot,
 #confirm-password-dot,
 #controller-pairing-dot,
 #debugging-dot,
 #device-disabled-dot,
 #enrollment-dot,
 #error-message-dot,
 #fatal-error-dot,
 #hid-detection-dot,
@@ skipping 66 matching lines @@
   line-height: 31px;
   text-transform: lowercase;
   width: 23em;
 }
 
 .header-section::before {
   /* Divider in header between product name and title,
    * like "[Product name] > [step header]". */
   content: '\00A0\203A\00A0\00A0';
 }