Oilpan: fix build after r182077.

TBR=oilpan-reviews
BUG=390125
NOTRY=true

Review URL: https://codereview.chromium.org/572933005

git-svn-id: svn://svn.chromium.org/blink/trunk@182104 bbb929c8-8fbe-4397-9dbb-9b2b20218538