Fix use of uninitialized raw pointer in oilpan build.

TBR=dstockwell@chromium.org, haraken@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/220663003

git-svn-id: svn://svn.chromium.org/blink/trunk@170545 bbb929c8-8fbe-4397-9dbb-9b2b20218538