[SVG] SVGAnimatedColor migration to new SVG property impl.

This CL replaces SVGAnimatedColorAnimator with NewSVGProperty based implementation, SVGColorProperty.

As SVGColor DOM interface is already deprecated in Blink, so this only affects SMIL animator implementation.
This CL will unify SVGColor animation path to use the SVGAnimateNewPropertyAnimator so that we can deprecate old SMIL animator.

Also, this CL don't touch the SVGColor class, which is currently a CSSValue.
Instead, we introduce a new class SVGColorProperty which directly operates on StyleColor.

When SMIL is implemented in WebAnimation, we should be able to replace SVGColorProperty with AnimatedColor.
This CL is intended to be a temporary solution.

For details, see design doc: https://docs.google.com/document/d/1bg7CUyUszqdwmENY3JX6_PoQD6uHRCNcRPJMlC4qlkw/edit?usp=sharing

BUG=308818

Review URL: https://codereview.chromium.org/148053002

git-svn-id: svn://svn.chromium.org/blink/trunk@166135 bbb929c8-8fbe-4397-9dbb-9b2b20218538