Oilpan: Fix Oilpan build for GCC after r171244.

TBR=tkent@chromium.org
BUG=

Review URL: https://codereview.chromium.org/232763002

git-svn-id: svn://svn.chromium.org/blink/trunk@171247 bbb929c8-8fbe-4397-9dbb-9b2b20218538