LibWeb: Parse the border-image-slice property

Author: https://github.com/tcl3
Commit: 245905b833
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/5253
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/CSSStyleValue.h

@@ -90,6 +90,7 @@ public:
         Angle,
         BackgroundRepeat,
         BackgroundSize,
+        BorderImageSlice,
         BasicShape,
         BorderRadius,
         Calculated,
@@ -169,6 +170,10 @@ public:
     BasicShapeStyleValue const& as_basic_shape() const;
     BasicShapeStyleValue& as_basic_shape() { return const_cast<BasicShapeStyleValue&>(const_cast<CSSStyleValue const&>(*this).as_basic_shape()); }
 
+    bool is_border_image_slice() const { return type() == Type::BorderImageSlice; }
+    BorderImageSliceStyleValue const& as_border_image_slice() const;
+    BorderImageSliceStyleValue& as_border_image_slice() { return const_cast<BorderImageSliceStyleValue&>(const_cast<CSSStyleValue const&>(*this).as_border_image_slice()); }
+
     bool is_border_radius() const { return type() == Type::BorderRadius; }
     BorderRadiusStyleValue const& as_border_radius() const;
     BorderRadiusStyleValue& as_border_radius() { return const_cast<BorderRadiusStyleValue&>(const_cast<CSSStyleValue const&>(*this).as_border_radius()); }