[cssom-view] Add more enumeration values to CSSBoxType for SVG

Hi,

I was looking at the GeometryUtils API and specifically at the enumeration CSSBoxType[1].

Currently CSSBoxType supports the enumeration values: "margin", "border", "padding", “content”. We already had a discussion for CSS Masking that these values are not sufficient for SVG. In SVG we added the keywords: "fill-box", "stroke-box" and “view-box” [2]. (The suffix “-box" is there for consistency with decisions made for CSS2.)

I wonder if it makes sense to add “fill”, “stroke” and “view” to CSSBoxType. However, the BoxQuadOptions and ConvertCoordinateOptions have initial values for their box types that are “border”. In CSS Masking we say that "margin", "border", "padding", “content” are mapped to “fill” for SVG elements and “fill”, “stroke”, “view” are mapped to the initial values of the properties (“border”).

Greetings,
Dirk

[1] http://dev.w3.org/csswg/cssom-view/#the-geometryutils-interface
[2] http://www.w3.org/TR/css-masking-1/#the-mask-clip