Oilpan: fix build after r178904.

R=haraken@chromium.org
BUG=373120
NOTRY=true

Review URL: https://codereview.chromium.org/422473002

git-svn-id: svn://svn.chromium.org/blink/trunk@178909 bbb929c8-8fbe-4397-9dbb-9b2b20218538