Mark when we may have been invalidated to early out on repaintTreeAfterLayout.

Source/core/rendering/RenderListBox.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  *               2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 174 matching lines @@
 
     if (AXObjectCache* cache = document().existingAXObjectCache())
         cache->selectedChildrenChanged(this);
 }
 
 void RenderListBox::layout()
 {
     RenderBlockFlow::layout();
 
     if (m_vBar) {
+        setMayNeedInvalidation(true);
+
         bool enabled = numVisibleItems() < numItems();
         m_vBar->setEnabled(enabled);
         m_vBar->setProportion(numVisibleItems(), numItems());
         if (!enabled) {
             scrollToOffsetWithoutAnimation(VerticalScrollbar, 0);
             m_indexOffset = 0;
         }
     }
 
     if (m_scrollToRevealSelectionAfterLayout) {
+        setMayNeedInvalidation(true);
+
         LayoutStateDisabler layoutStateDisabler(*this);
         scrollToRevealSelection();
     }
 }
 
 void RenderListBox::repaintTreeAfterLayout()
 {
     repaintScrollbarIfNeeded();
     RenderBox::repaintTreeAfterLayout();
 }
@@ skipping 807 matching lines @@
 {
     return itemBoundingBoxRectInternal(point, listIndexToRenderListBoxIndex(index));
 }
 
 bool RenderListBox::scrollToRevealElementAtListIndex(int index)
 {
     return scrollToRevealElementAtListIndexInternal(listIndexToRenderListBoxIndex(index));
 }
 
 } // namespace WebCore