Oilpan: fix build after r181280.

R=haraken
BUG=396372
NOTRY=true

Review URL: https://codereview.chromium.org/535733003

git-svn-id: svn://svn.chromium.org/blink/trunk@181284 bbb929c8-8fbe-4397-9dbb-9b2b20218538