Reviewed by Kevin.

    Reviewed by Kevin.

	- fixed <rdar://problem/3878183> Safari is 77% slower than it should be on a page on an IBM website due to NodeListImpl length

	I fixed this by changing NodeLists to cache their length, but
	invalidate it whenever there is a change in the DOM subtree at
	which they are rooted. This makes NodeListImpl::recursiveLength()
	drop completely off the profile, since we were repeatedly getting
	a length for the same NodeList over and over.

        * khtml/xml/dom_nodeimpl.cpp:
        (NodeImpl::NodeImpl):
        (NodeImpl::~NodeImpl):
        (NodeImpl::registerNodeList):
        (NodeImpl::unregisterNodeList):
        (NodeImpl::notifyLocalNodeListsSubtreeModified):
        (NodeImpl::notifyNodeListsSubtreeModified):
        (NodeImpl::dispatchSubtreeModifiedEvent):
        (NodeListImpl::NodeListImpl):
        (NodeListImpl::~NodeListImpl):
        (NodeListImpl::recursiveLength):
        (NodeListImpl::recursiveItem):
        (NodeListImpl::rootNodeSubtreeModified):
        (ChildNodeListImpl::ChildNodeListImpl):
        (ChildNodeListImpl::length):
        (ChildNodeListImpl::item):
        (TagNodeListImpl::TagNodeListImpl):
        (TagNodeListImpl::length):
        (TagNodeListImpl::item):
        (NameNodeListImpl::NameNodeListImpl):
        (NameNodeListImpl::length):
        (NameNodeListImpl::item):
        * khtml/xml/dom_nodeimpl.h:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@7997 268f45cc-cd09-0410-ab3c-d52691b4dbfc