Oilpan: fix use of uninitialized raw pointers on the stack.

These are crashing on layout tests in the oilpan build. The reason is
that with oilpan these are just raw pointers and are therefore not
default initialized to null.

R=haraken@chromium.org, oilpan-reviews@chromium.org, timloh@chromium.org

Review URL: https://codereview.chromium.org/473163002

git-svn-id: svn://svn.chromium.org/blink/trunk@180340 bbb929c8-8fbe-4397-9dbb-9b2b20218538