Oilpan: fix for r173953.

TBR=kouhei@chromium.org
BUG=

Review URL: https://codereview.chromium.org/279383008

git-svn-id: svn://svn.chromium.org/blink/trunk@173971 bbb929c8-8fbe-4397-9dbb-9b2b20218538