Oilpan: update WebNotification and WebDOMMediaStreamTrack type conversions

These two public/web/ types hadn't been updated to use transition types
over their underlying Oilpan-converted objects.

R=tkent@chromium.org,haraken@chromium.org
BUG=357163

Review URL: https://codereview.chromium.org/310393004

git-svn-id: svn://svn.chromium.org/blink/trunk@175540 bbb929c8-8fbe-4397-9dbb-9b2b20218538