Reviewed by Darin Adler.

PseudoElement sets its host node as its parent. This is confusing and wrong as it breaks
the basic tree consistency (a node is a child node of its parent node).
        
This patch adds an explicit host pointer PseudoElement and switches the call sites over. Memory
impact is negligible as there are not that many ::befores and ::afters.

* dom/ComposedShadowTreeWalker.cpp:
(WebCore::ComposedShadowTreeWalker::traverseParent):
* dom/EventPathWalker.cpp:
(WebCore::EventPathWalker::moveToParent):
* dom/EventRetargeter.h:
(WebCore::EventRetargeter::eventTargetRespectingTargetRules):
* dom/Node.cpp:
(WebCore::Node::~Node):
        
    Add consistency assertions. Remove unnecessary clearing of sibling pointers. They should be cleared already.

(WebCore::Node::markAncestorsWithChildNeedsStyleRecalc):
* dom/PseudoElement.cpp:
(WebCore::PseudoElement::PseudoElement):
(WebCore::PseudoElement::customStyleForRenderer):
* dom/PseudoElement.h:
(WebCore::toPseudoElement):
        
    Add casting functions.

* inspector/InspectorLayerTreeAgent.cpp:
(WebCore::InspectorLayerTreeAgent::buildObjectForLayer):
* rendering/HitTestResult.cpp:
(WebCore::HitTestResult::setInnerNode):
(WebCore::HitTestResult::setInnerNonSharedNode):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154232 268f45cc-cd09-0410-ab3c-d52691b4dbfc