Oilpan: fix build after r184599.

TBR=oilpan-reviews,haraken
BUG=425186
NOTRY=true

Review URL: https://codereview.chromium.org/691613002

git-svn-id: svn://svn.chromium.org/blink/trunk@184601 bbb929c8-8fbe-4397-9dbb-9b2b20218538