Add Oilpan heap object headers.

Will start pulling things in so we can get objects allocated
in the oilpan heap with Persistent handles to them.

R=vegorov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/99923006

git-svn-id: svn://svn.chromium.org/blink/trunk@163786 bbb929c8-8fbe-4397-9dbb-9b2b20218538