bindings: Makes SVGAnimatedProperty ScriptWrappable.

Makes SVGAnimatedProperty and its subclasses inherit from ScriptWrappable.
This change increases the size of SVGAnimatedProperty and its subclasses
by 8 bytes (on 64-bit env).

BUG=235436

Review URL: https://codereview.chromium.org/720113003

git-svn-id: svn://svn.chromium.org/blink/trunk@185346 bbb929c8-8fbe-4397-9dbb-9b2b20218538