[SVG] SVGAnimatedRect migration to new SVG property impl.

This CL replaces SVGAnimatedRect class with NewSVGProperty implementation.

This CL changes the behavior of SVGViewSpec.viewBox readonly animated property.
In the previous implementation, changes to readonly property was silently ignored.
This CL uses new implementation of animated property which follows the spec.
It throws exception when they are tried to be modified.

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

BUG=308818
R=haraken@chromium.org, pdr@chromium.org

Review URL: https://codereview.chromium.org/132233010

git-svn-id: svn://svn.chromium.org/blink/trunk@165382 bbb929c8-8fbe-4397-9dbb-9b2b20218538