Oilpan: move Node traversal objects to the heap.

Add Oilpan transition types to NodeIterator, TreeIterator and
NodeFilter objects.

R=haraken@chromium.org
BUG=357163

Review URL: https://codereview.chromium.org/285213003

git-svn-id: svn://svn.chromium.org/blink/trunk@174262 bbb929c8-8fbe-4397-9dbb-9b2b20218538