Oilpan: Fix build broken by r172717

TBR=haraken@chromium.org
BUG=

Review URL: https://codereview.chromium.org/251923002

git-svn-id: svn://svn.chromium.org/blink/trunk@172723 bbb929c8-8fbe-4397-9dbb-9b2b20218538