Oilpan: fix build after r178153.

R=haraken@chromium.org
BUG=169721
NOTRY=true

Review URL: https://codereview.chromium.org/395623007

git-svn-id: svn://svn.chromium.org/blink/trunk@178156 bbb929c8-8fbe-4397-9dbb-9b2b20218538