Oilpan: Fix oilpan build after r177275

TBR=haraken@chromium.org,oilpan-reviews@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/363513005

git-svn-id: svn://svn.chromium.org/blink/trunk@177295 bbb929c8-8fbe-4397-9dbb-9b2b20218538