Remove AttrNodeListMap.

Change the ownership of AttrNodeList from a static HashMap to ElementRareData.

ElementRareData size increases by this change. A complex web page will
have slight increase of memory consumption even if the page doesn't
use Attr nodes.

BUG=357163,381629

Review URL: https://codereview.chromium.org/328243005

git-svn-id: svn://svn.chromium.org/blink/trunk@176366 bbb929c8-8fbe-4397-9dbb-9b2b20218538