Oilpan: convert remaining editing/ RefPtr<Node>s to transition types.

Remove unnecessary uses of RefPtr<Node>s with Oilpan enabled.

R=zerny@chromium.org,ager@chromium.org
BUG=357163

Review URL: https://codereview.chromium.org/309283002

git-svn-id: svn://svn.chromium.org/blink/trunk@175378 bbb929c8-8fbe-4397-9dbb-9b2b20218538