Use relative bounding boxes throughout Chrome accessibility

chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs

 // Copyright 2014 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.
 
 // Include test fixture.
 GEN_INCLUDE(['../../testing/chromevox_next_e2e_test_base.js',
              '../../testing/assert_additions.js']);
 
 GEN_INCLUDE(['../../testing/mock_feedback.js']);
 
@@ skipping 63 matching lines @@
 
   iframesDoc: function() {/*!
     <p>start</p>
     <button>Before</button>
     <iframe srcdoc="<button>Inside</button><h1>Inside</h1>"></iframe>
     <button>After</button>
   */},
 
   disappearingObjectDoc: function() {/*!
     <p>start</p>
-    <article>
+    <div role="group">

[aboxhall, 2016/08/12 16:05:10]

Why this change?

[dmazzoni, 2016/08/15 05:31:11]

A very obscure side effect of this change was that the
bounding box of the HTML <article> element with no children
had zero height before this patch, and nonzero height with
this patch, just due to differences in what functions we're
calling to compute the bounding box. With a nonzero bounding
box ChromeVox was landing on this element and saying "Article"
now, breaking the test. I just changed it to an element that
would still show up in the accessibility tree but would have
zero height when empty.

       <p>Before1</p>
       <p>Before2</p>
       <p>Before3</p>
-    </article>
-    <article>
+    </div>
+    <div role="group">
       <p id="disappearing">Disappearing</p>
-    </article>
-    <article>
+    </div>
+    <div role="group">
       <p>After1</p>
       <p>After2</p>
       <p>After3</p>
-    </article>
     </div>
     <div id="live" aria-live="polite"></div>
     <div id="delete" role="button">Delete</div>
     <script>
       document.getElementById('delete').addEventListener('click', function() {
         var d = document.getElementById('disappearing');
         d.parentElement.removeChild(d);
         document.getElementById('live').innerText = 'Deleted';
       });
     </script>
@@ skipping 999 matching lines @@
 });
 
 TEST_F('BackgroundTest', 'DisabledState', function() {
   var mockFeedback = this.createMockFeedback();
   this.runWithLoadedTree(function(root) {/*!
     <button aria-disabled="true">ok</button>
   */}, function(root) {
     mockFeedback.expectSpeech('ok', 'Disabled', 'Button').replay();
   });
 });