Oilpan: Update stack allocated class to use Member after namespace-fix for the Blink GC plugin.

R=haraken@chromium.org
BUG=

Review URL: https://codereview.chromium.org/299703007

git-svn-id: svn://svn.chromium.org/blink/trunk@174491 bbb929c8-8fbe-4397-9dbb-9b2b20218538