Oilpan: fix build after r182644.

TBR=oilpan-reviews, ddorwin@chromium.org
BUG=
NOTRY=true

Review URL: https://codereview.chromium.org/599093006

git-svn-id: svn://svn.chromium.org/blink/trunk@182654 bbb929c8-8fbe-4397-9dbb-9b2b20218538