Add "Show saved copy" button in dino page when there's offline copy

chrome/renderer/resources/neterror.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. */
 
 /* Don't use the main frame div when the error is in a subframe. */
 html[subframe] #main-frame-error {
   display: none;
 }
 
 /* Don't use the subframe error div when the error is in a main frame. */
@@ skipping 54 matching lines @@
 }
 
 .error-code {
   display: block;
 }
 
 #content-top {
   margin: 20px;
 }
 
+.gray-button {
+  background: #d9d9d9;
+  color: #696969;
+}
+
 #help-box-inner {
   background-color: #f9f9f9;
   border-top: 1px solid #EEE;
   color: #444;
   padding: 20px;
   text-align: start;
 }
 
 .hidden {
   display: none;
@@ skipping 360 matching lines @@
   .interstitial-wrapper {
     overflow: inherit;
     padding: 0 8px;
   }
 }
 
 @media (max-width: 120px) {
   button {
     width: auto;
   }
-}
+}