Componentize IDR_NET_ERROR_HTML for sharing it with iOS.

components/neterror/resources/neterror.js

 // 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.
 
 function toggleHelpBox() {
   var helpBoxOuter = document.getElementById('details');
   helpBoxOuter.classList.toggle('hidden');
   var detailsButton = document.getElementById('details-button');
   if (helpBoxOuter.classList.contains('hidden'))
     detailsButton.innerText = detailsButton.detailsText;
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     // Set the secondary button state in the cases of two call to actions.
     if ((reloadButtonVisible || showOfflinePagesButtonVisible ||
          showOfflineCopyButton) &&
         showSavedCopyButtonVisible) {
       secondaryButton.classList.add('secondary-button');
     }
   }
 }
 
 document.addEventListener('DOMContentLoaded', onDocumentLoad);