style: Define path() for clip-path.

For now, |clip-path: path()| is chrome-only, and not for shape-outside,
so we only implement the parser for clip-path. Besides, I didn't put
path() in BasicShape because path() doesn't use the reference box to
resolve the percentage or keywords (i.e. SVG path only accept floating
point or integer number as the css pixel value). Therefore, I add it into
ShapeSource, instead of BasicShape.

Differential Revision: https://phabricator.services.mozilla.com/D3633

components/style/values/generics/basic_shape.rs

@@ -12,6 +12,7 @@ use values::distance::{ComputeSquaredDistance, SquaredDistance};
 use values::generics::border::BorderRadius;
 use values::generics::position::Position;
 use values::generics::rect::Rect;
+use values::specified::SVGPathData;
 
 /// A clipping shape, for `clip-path`.
 pub type ClippingShape<BasicShape, Url> = ShapeSource<BasicShape, GeometryBox, Url>;
@@ -54,6 +55,9 @@ pub enum ShapeSource<BasicShape, ReferenceBox, ImageOrUrl> {
     #[animation(error)]
     Box(ReferenceBox),
     #[animation(error)]
+    #[css(function)]
+    Path(Path),
+    #[animation(error)]
     None,
 }
 
@@ -144,6 +148,19 @@ pub enum FillRule {
     Evenodd,
 }
 
+/// The path function defined in css-shape-2.
+///
+/// https://drafts.csswg.org/css-shapes-2/#funcdef-path
+#[css(comma)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
+pub struct Path {
+    /// The filling rule for the svg path.
+    #[css(skip_if = "fill_is_default")]
+    pub fill: FillRule,
+    /// The svg path data.
+    pub path: SVGPathData,
+}
+
 // FIXME(nox): Implement ComputeSquaredDistance for T types and stop
 // using PartialEq here, this will let us derive this impl.
 impl<B, T, U> ComputeSquaredDistance for ShapeSource<B, T, U>