Oilpan: fix build after r181322

R=haraken
BUG=399178
NOTRY=true

Review URL: https://codereview.chromium.org/534253004

git-svn-id: svn://svn.chromium.org/blink/trunk@181334 bbb929c8-8fbe-4397-9dbb-9b2b20218538