Oilpan: fix build after r177509.

TBR=haraken@chromium.org
BUG=383813
NOTRY=true

Review URL: https://codereview.chromium.org/370693002

git-svn-id: svn://svn.chromium.org/blink/trunk@177512 bbb929c8-8fbe-4397-9dbb-9b2b20218538