Oilpan: Add RawPtr version of DictionaryHelper::get for Path2D.

TBR=bashi@chromium.org, sigbjornf@opera.com
NOTRY=true

Review URL: https://codereview.chromium.org/579703002

git-svn-id: svn://svn.chromium.org/blink/trunk@182144 bbb929c8-8fbe-4397-9dbb-9b2b20218538