Oilpan: fix build after r183810.

R=haraken
BUG=393913
NOTRY=true

Review URL: https://codereview.chromium.org/662633002

git-svn-id: svn://svn.chromium.org/blink/trunk@183814 bbb929c8-8fbe-4397-9dbb-9b2b20218538