Use relative bounding boxes throughout Chrome accessibility

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

Index: chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs
diff --git a/chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs b/chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs
index f277a97487911450cd34dfddcbdb3f0acbf40513..61990f82275a59470e7adc098f620ecb3018b4c8 100644
--- a/chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs
+++ b/chrome/browser/resources/chromeos/chromevox/cvox2/background/background_test.extjs
@@ -81,19 +81,18 @@ BackgroundTest.prototype = {
 
   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>