Oilpan: fix (release) builds after r180088.

R=haraken
BUG=340522
NOTRY=true

Review URL: https://codereview.chromium.org/469713002

git-svn-id: svn://svn.chromium.org/blink/trunk@180149 bbb929c8-8fbe-4397-9dbb-9b2b20218538