Refactor kiosk app launch to be part of login screen UI flow.

chrome/browser/resources/chromeos/login/oobe_screen.css

 /* Copyright 2013 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.
  *
  * This contains common styling for all the OOBE screens.
  */
 
 .step {
   box-sizing: border-box;
   position: absolute;
@@ skipping 16 matching lines @@
 }
 
 .step.right {
   -webkit-transform: translateX(50px);
 }
 
 .step.left {
   -webkit-transform: translateX(-50px)
 }
 
+.step.fullscreen {
+  height: 100%;
+  left: 0;
+  right: 0;
+  top: 0;
+  width: 100%;
+}
+
 .step-controls {
   -webkit-box-pack: end;
   -webkit-padding-end: 34px;  /* Double the padding of .step */
   bottom: 21px;
   box-sizing: border-box;
   display: -webkit-box;
   height: 28px;
   position: absolute;
   width: 100%;
 }
@@ skipping 114 matching lines @@
 }
 
 html[highlight=strong] #security-info a:focus,
 html[highlight=strong] #eula a:focus,
 html[highlight=strong] .step-extra-controls a:focus,
 html[highlight=strong] .menu-control:focus,
 html[highlight=strong] input[type='button']:focus,
 html[highlight=strong] button:focus {
   box-shadow: 0 0 23px rgb(77, 144, 254) !important;
 }