Fix Oilpan build broken by r179290.

TBR=loislo@chromium.org, oilpan-reviews@chromium.org
BUG=

Review URL: https://codereview.chromium.org/433773003

git-svn-id: svn://svn.chromium.org/blink/trunk@179294 bbb929c8-8fbe-4397-9dbb-9b2b20218538