Oilpan: Replace all of RefPtrs of CharacterData, Comment, DocumentType, and ProcessingInstruction with Oilpan transition types.

BUG=357163

Review URL: https://codereview.chromium.org/286633003

git-svn-id: svn://svn.chromium.org/blink/trunk@173951 bbb929c8-8fbe-4397-9dbb-9b2b20218538