Oilpan build fix: Rawptr should be explicitly initialized

BUG=None
R=keishi@chromium.org

Review URL: https://codereview.chromium.org/378773002

git-svn-id: svn://svn.chromium.org/blink/trunk@177631 bbb929c8-8fbe-4397-9dbb-9b2b20218538