Oilpan: move SVG property hierarchy to the heap.

Turn SVGPropertyBase into a non-refcounted, GCed object
and move all its derived objects to the heap.

R=kouhei,haraken
BUG=340522

Review URL: https://codereview.chromium.org/678163002

git-svn-id: svn://svn.chromium.org/blink/trunk@185240 bbb929c8-8fbe-4397-9dbb-9b2b20218538