Move isNameCacheValid member from LiveNodeListBase to HTMLCollection

The isNameCacheValid member is only useful to HTMLCollection (not LiveNodeList),
so move it and its corresponding getter / setter to the HTMLCollection class.
There is no reason anymore to keep this member in the LiveNodeListBase class.

R=eseidel, esprehn
BUG=None

Review URL: https://codereview.chromium.org/130753004

git-svn-id: svn://svn.chromium.org/blink/trunk@165248 bbb929c8-8fbe-4397-9dbb-9b2b20218538