ChromeOS: Implement Language Selection screen of material design OOBE.

chrome/browser/resources/chromeos/login/oobe_dialog.html

 <!-- Copyright 2016 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. -->
 
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/color.html">
 
 <!--
   Simple OOBE card which should be used for OOBE UI elements.
   It has blue header and grey footer.
 
   Example:
     <oobe-dialog>
       <iron-icon ... class="oobe-icon">
       <div class="header flex vertical layout end-justified start">
         ...
       </div>
       <oobe-input-form class="footer" ...>
       </oobe-input-form>
+      <oobe-text-button class="footer" label="OK" ...>
+      </oobe-text-button>
     </oobe-dialog>
 
   Add class |header| to all which you want to go inside the header.  Similar
   with clases |footer| and |oobe-icon|.
 -->
 <dom-module name="oobe-dialog">
   <link rel="stylesheet" href="oobe_dialog.css">
   <template>
     <div class="oobe-header vertical layout relative">
       <div class="header-container flex vertical layout relative">
         <div class="oobe-icon-div">
           <content select=".oobe-icon"></content>
         </div>
         <content select=".header"></content>
       </div>
     </div>
     <div class="oobe-footer flex vertical layout">
       <div class="footer-container flex vertical layout">
         <content select=".footer"></content>
       </div>
-      <div id="bottom-overlay" class="overlay"></div>
     </div>
-    <div id="full-overlay" class="overlay"></div>
+    <template is="dom-if" if="[[hasButtons]]">
+      <div id="oobe-bottom" class="layout horizontal end-justified">
+        <content select=".bottom-buttons"></content>
+      </div>
+    </template>
   </template>
 </dom-module>