List marker pseudo elements.

Source/core/html/HTMLOListElement.cpp

Index: Source/core/html/HTMLOListElement.cpp
diff --git a/Source/core/html/HTMLOListElement.cpp b/Source/core/html/HTMLOListElement.cpp
index 4da5176a545b3d09689ce83c8e5da11c6da56275..4698aef14c8851fb1a147802ca15ec8f5d047a55 100644
--- a/Source/core/html/HTMLOListElement.cpp
+++ b/Source/core/html/HTMLOListElement.cpp
@@ -108,4 +108,21 @@ void HTMLOListElement::recalculateItemCount()
     m_shouldRecalculateItemCount = false;
 }
 
+void HTMLOListElement::attach(const AttachContext& context)
+{
+    HTMLElement::attach(context);
+
+    if (!RuntimeEnabledFeatures::listMarkerPseudoElementEnabled())
+        return;
+
+    if (!m_isReversed)
+        return;
+
+    // If we're looking at a reversed ordered list we have to recalculate
+    // all of the marker values after everything is inserted. This is because
+    // we built the tree top to bottom, but that means the list item with the
+    // highest value will end up with 1 and we count down from there.
+    updateItemValues();

[esprehn, 2015/04/22 07:45:45]

Why is this needed? All updateItemValues does is:
updateItemValuesForOrderedList

which goes into each list item doing:

    if (!m_hasExplicitValue) {
        m_isValueUpToDate = false;
        if (m_marker)
           
m_marker->setNeedsLayoutAndPrefWidthsRecalcAndFullPaintInvalidation(LayoutInvalidationReason::ListValueChange);
    }

but every list item is brand new, we just attached them, that means they all
need layout already, all need paint invalidation, and the m_isValueUpToDate
field starts as false. So this shouldn't do anything.

[dsinclair, 2015/04/22 20:00:39]

This works fine for lists that aren't reversed. The problem is, with a reversed
list we do something along the lines of:

- add first item, see only one item, set value to 1
- add second item, see previous was 1, set value to 0
- ...

We quickly end up with negative list values. There is logic in
LayoutListItem::updateListMarkerNumbers which tells it to not call updateValue()
if listNode->needsAttach(). Adding this call here means we can do one walk to
update all of the values for reverse lists at the same time and should save the
O(n^2) walk to do it as we attach.

+}
+
 }