Oilpan: build fix followup to r170842.

R=
BUG=340522
NOTRY=true

Review URL: https://codereview.chromium.org/225783002

git-svn-id: svn://svn.chromium.org/blink/trunk@170857 bbb929c8-8fbe-4397-9dbb-9b2b20218538