Micro-optimize the way we hand NodeLists to JSC.

Micro-optimize the way we hand NodeLists to JSC.
<https://webkit.org/b/131932>

Use HashMap::fastAdd() when returning cached node lists and collections.
10.9% progression on Bindings/get-elements-by-tag-name.html

Reviewed by Antti Koivisto.

* dom/NodeRareData.h:
(WebCore::NodeListsNodeData::addCacheWithAtomicName):
(WebCore::NodeListsNodeData::addCacheWithName):
(WebCore::NodeListsNodeData::addCacheWithQualifiedName):
(WebCore::NodeListsNodeData::addCachedCollection):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167589 268f45cc-cd09-0410-ab3c-d52691b4dbfc