compareDocumentPosition() should report PRECEEDING or FOLLOWING information even if nodes are disconnected

As per the latest specification, compareDocumentPosition() should report PRECEEDING or FOLLOWING
information even if nodes are disconnected:
- http://dom.spec.whatwg.org/#dom-node-comparedocumentposition

This behavior is consistent with both IE10 and Firefox 22.

Blink was not reporting PRECEEDING or FOLLOWING in all cases. This patches makes Blink behave
as expected.

BUG=263340
R=arv@chromium.org, haraken@chromium.org, tkent@chromium.org

Review URL: https://codereview.chromium.org/20042003

git-svn-id: svn://svn.chromium.org/blink/trunk@154835 bbb929c8-8fbe-4397-9dbb-9b2b20218538