Adds a new checkbox for backup and restore in opt-in flow.

chrome/browser/resources/chromeos/arc_support/main.css

 /**
  * 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.
  */
 
 html,
 body,
 webview,
 .section {
   font-family: 'Roboto';
   height: 100%;
   margin: 0;
   padding: 0;
   width: 100%;
 }
 
 #arc-support {
   padding: 0;
 }
 
 .button-separator {
   width: 1px;
 }
 
-.checkbox-metrics {
+.checkbox-option {
   height: 16px;
   margin: 0;
   padding: 0 8px 0 0;
   width: 16px;
 }
 
 .image-header {
   display: block;
   height: 300px;
   padding: 0;
   width: 960px;
 }
 
 .section {
   text-align: center;
 }
 
 .section-buttons {
   margin: auto;
   padding: 16px 0 24px 0;
   width: 468px;
 }
 
 .section-flex {
   display: flex;
   flex-direction: column;
   height: 688px;
 }
 
-.section-metrics {
+.section-checkbox-container {
   margin: auto;
   padding: 16px 0 0 0;
   text-align: left;
   width: 468px;
 }
 
 .section-terms {
   border: 1px solid #e6e6e6;
   color: rgba(0, 0, 0, 0.54);
   flex: auto;
   margin: auto;
   overflow: hidden;
   padding: 0;
   width: 468px;
 }
 
 .text-desc {
   color: rgba(0, 0, 0, 0.54);
   font-size: 18px;
   font-weight: 300;
   line-height: 24px;
   margin: auto;
   padding: 16px 0 0 0;
   width: 600px;
 }
 
-.text-metrics {
+.checkbox-text {
   color: rgba(0, 0, 0, 0.54);
   font-size: 10px;
   font-weight: 400;
   line-height: 16px;
   margin: 0;
   padding: 0;
 }
 
 .text-status {
   color: rgba(0, 0, 0, 0.54);
@@ skipping 25 matching lines @@
 
 a:link {
   color: rgb(51, 103, 214);
   text-decoration: none;
 }
 
 a:visited {
   color: rgb(51, 103, 214);
   text-decoration: none;
 }