C++11: Replace 0 with nullptr where applicable in layout code.

Source/core/layout/LayoutObjectChildList.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 85 matching lines @@
     if (oldChild->previousSibling())
         oldChild->previousSibling()->setNextSibling(oldChild->nextSibling());
     if (oldChild->nextSibling())
         oldChild->nextSibling()->setPreviousSibling(oldChild->previousSibling());
 
     if (firstChild() == oldChild)
         setFirstChild(oldChild->nextSibling());
     if (lastChild() == oldChild)
         setLastChild(oldChild->previousSibling());
 
-    oldChild->setPreviousSibling(0);
-    oldChild->setNextSibling(0);
-    oldChild->setParent(0);
+    oldChild->setPreviousSibling(nullptr);
+    oldChild->setNextSibling(nullptr);
+    oldChild->setParent(nullptr);
 
     oldChild->registerSubtreeChangeListenerOnDescendants(oldChild->consumesSubtreeChangeNotification());
 
     if (AXObjectCache* cache = owner->document().existingAXObjectCache())
         cache->childrenChanged(owner);
 
     return oldChild;
 }
 
 void LayoutObjectChildList::insertChildNode(LayoutObject* owner, LayoutObject* newChild, LayoutObject* beforeChild, bool notifyLayoutObject)
@@ skipping 71 matching lines @@
     DisableCompositingQueryAsserts disabler;
     // FIXME: We should not allow paint invalidation out of paint invalidation state. crbug.com/457415
     DisablePaintInvalidationStateAsserts paintInvalidationAssertDisabler;
     const LayoutBoxModelObject& paintInvalidationContainer = *oldChild.containerForPaintInvalidation();
     oldChild.invalidatePaintUsingContainer(paintInvalidationContainer, oldChild.previousPaintInvalidationRect(), PaintInvalidationLayoutObjectRemoval);
     if (RuntimeEnabledFeatures::slimmingPaintEnabled())
         oldChild.invalidateDisplayItemClients(paintInvalidationContainer);
 }
 
 } // namespace blink