Oilpan: fix build after r175732.

Restore equality test back to being between Node* and a RawPtr<Node>,
for which there is an implicit conversion from a RawPtr<Node> to a
Node*. i.e., a RawPtr<Node> cannot be implicitly converted to a Node&
(and vice versa.)

TBR=haraken@chromium.org,oilpan-reviews@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/325573002

git-svn-id: svn://svn.chromium.org/blink/trunk@175745 bbb929c8-8fbe-4397-9dbb-9b2b20218538