Switch UseCounter to take a Document const ref instead of a pointer

This gets rid of many instances of "&document()" from core.

A few callers have been switched to the DOMWindow versions (for those
cases where the existence of a Document is not certain). This required
making the UseCounter take a const DOMWindow* (which works fine, since
DOMWindow::document() is const).

R=esprehn@chromium.org

Review URL: https://codereview.chromium.org/24330002

git-svn-id: svn://svn.chromium.org/blink/trunk@159485 bbb929c8-8fbe-4397-9dbb-9b2b20218538