Oilpan: fix build after r182688.

TBR=haraken
BUG=348919
NOTRY=true

Review URL: https://codereview.chromium.org/602183002

git-svn-id: svn://svn.chromium.org/blink/trunk@182701 bbb929c8-8fbe-4397-9dbb-9b2b20218538