Oilpan: avoid invoking some no-op finalizers.

Derive from GarbageCollected<> instead whenever possible.

R=haraken
BUG=340522

Review URL: https://codereview.chromium.org/697893003

git-svn-id: svn://svn.chromium.org/blink/trunk@185218 bbb929c8-8fbe-4397-9dbb-9b2b20218538