Support presentational iframes and make use of them in the uber frame.

chrome/browser/resources/uber/uber.js

 // Copyright (c) 2012 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.
 
 cr.define('uber', function() {
   /**
    * Options for how web history should be handled.
    */
   var HISTORY_STATE_OPTION = {
     PUSH: 1,    // Push a new history state.
@@ skipping 319 matching lines @@
    */
   function showPage(pageId, historyOption, path) {
     var container = $(pageId);
 
     // Lazy load of iframe contents.
     var sourceUrl = container.dataset.url + (path || '');
     var frame = container.querySelector('iframe');
     if (!frame) {
       frame = container.ownerDocument.createElement('iframe');
       frame.name = pageId;
+      frame.setAttribute('role', 'presentation');
       container.appendChild(frame);
       frame.src = sourceUrl;
     } else {
       // There's no particularly good way to know what the current URL of the
       // content frame is as we don't have access to its contentWindow's
       // location, so just replace every time until necessary to do otherwise.
       frame.contentWindow.location.replace(sourceUrl);
       frame.dataset.ready = false;
     }
 
@@ skipping 116 matching lines @@
   }
 
   return {
     onLoad: onLoad,
     onPopHistoryState: onPopHistoryState
   };
 });
 
 window.addEventListener('popstate', uber.onPopHistoryState);
 document.addEventListener('DOMContentLoaded', uber.onLoad);