SVGElement::parseAttribute resolves property via property map (Step 1)

This CL introduces |SVGElement::parseAttributeNew|, a new
|SVGElement::parseAttribute| implementation based on property map.

Before this patch, |SVG(.*)Element::parseAttribute| used chained if stmts
to resolve SVGAnimatedProperty. This patch changes it to resolve using
property map.

This is to replace the existing |SVGElement::parseAttribute| implementation,
but as there are many callers, we would like to proceed this incrementally.
a) Introduce |SVGElement::parseAttributeNew|
b) Convert all overrides |SVGElement::parseAttribute| to
   a |parseAttributeNew| call.
c) Replace existing |parseAttribute| with |parseAttributeNew|, and remove all
   overrides simply calling |parseAttributeNew|

This patch is (a). This patch also converts |SVG{Graphics,Rect}Element::parseAttribute| to start with (b).

BUG=397902

Review URL: https://codereview.chromium.org/421863002

git-svn-id: svn://svn.chromium.org/blink/trunk@179019 bbb929c8-8fbe-4397-9dbb-9b2b20218538