DynamicNodeList: Simplify internal Caches object.

DynamicNodeList: Simplify internal Caches object.
<http://webkit.org/b/76600>

Reviewed by Ryosuke Niwa.

Move m_caches from DynamicSubtreeNodeList and ChildNodeList up into DynamicNodeList.
Remove the inheritance from RefCounted and store it simply as "Caches m_caches"
This avoids one heap allocation per DynamicNodeList. Also reordered the Caches members
to pack slightly better on 64-bit.

* dom/ChildNodeList.cpp:
(WebCore::ChildNodeList::ChildNodeList):
(WebCore::ChildNodeList::length):
(WebCore::ChildNodeList::item):
* dom/ChildNodeList.h:
* dom/DynamicNodeList.cpp:
(WebCore::DynamicSubtreeNodeList::DynamicSubtreeNodeList):
(WebCore::DynamicSubtreeNodeList::length):
(WebCore::DynamicSubtreeNodeList::itemForwardsFromCurrent):
(WebCore::DynamicSubtreeNodeList::itemBackwardsFromCurrent):
(WebCore::DynamicSubtreeNodeList::item):
* dom/DynamicNodeList.h:
(WebCore::DynamicNodeList::invalidateCache):
* dom/Node.cpp:
(WebCore::NodeRareData::clearChildNodeListCache):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105408 268f45cc-cd09-0410-ab3c-d52691b4dbfc