Oilpan: fix build after r185293.

R=haraken
BUG=430337
NOTRY=true

Review URL: https://codereview.chromium.org/724083002

git-svn-id: svn://svn.chromium.org/blink/trunk@185302 bbb929c8-8fbe-4397-9dbb-9b2b20218538