Add use counters to Attr members removed in DOM4.

This is to gather evidence of what (if anything) can be deprecated and
removed from Attr. The relevant spec is here:

<http://dom.spec.whatwg.org/#interface-attr>

BUG=305105
R=eseidel@chromium.org

Review URL: https://codereview.chromium.org/26463002

git-svn-id: svn://svn.chromium.org/blink/trunk@159704 bbb929c8-8fbe-4397-9dbb-9b2b20218538