Add an intermediate function to generate 2 paint-order lists.

LayoutTests/compositing/overflow/resources/build-paint-order-lists.js

+function getPaintOrder(element)
+{
+  var divElementsBeforePromote = [];
+  var divElementsAfterPromote = [];
+  // Force a style recalc.
+  document.body.offsetTop;
+
+  var paintOrderListBeforePromote = window.internals.paintOrderListBeforePromote(element);
+  var paintOrderListAfterPromote = window.internals.paintOrderListAfterPromote(element);
+
+  for (var i = 0; i < paintOrderListBeforePromote.length; ++i)
+    if (paintOrderListBeforePromote[i].nodeName === "DIV")
+      divElementsBeforePromote.push(paintOrderListBeforePromote[i]);
+
+  for (var i = 0; i < paintOrderListAfterPromote.length; ++i)
+    if (paintOrderListAfterPromote[i].nodeName === "DIV")
+      divElementsAfterPromote.push(paintOrderListAfterPromote[i]);
+
+  return {"beforePromote": divElementsBeforePromote,
+          "afterPromote": divElementsAfterPromote};
+}
+
+function comparePaintOrderLists(oldPaintOrder, newPaintOrder)
+{
+  if (oldPaintOrder.length !== newPaintOrder.length)
+    return false;
+
+  for (var i = 0; i < oldPaintOrder.length; i++)
+    if (oldPaintOrder[i] !== newPaintOrder[i])
+      return false;
+
+  return true;
+}
+
+function countOccurrencesOfElementInPaintOrderList(paintOrder, element) {
+  var occurrenceCount = 0;
+  for (var i = 0; i < paintOrder.length; i++)
+    if (paintOrder[i] === element)
+      occurrenceCount++;
+
+  return occurrenceCount;
+}