Oilpan: fix build after r183495.

TBR=haraken
BUG=389249
NOTRY=true

Review URL: https://codereview.chromium.org/648543004

git-svn-id: svn://svn.chromium.org/blink/trunk@183512 bbb929c8-8fbe-4397-9dbb-9b2b20218538