stylo: Support -x-span for <col span>

components/style/properties/gecko.mako.rs

@@ -2230,6 +2230,15 @@ fn static_assert() {
 
 </%self:impl_trait>
 
+<%self:impl_trait style_struct_name="Table" skip_longhands="-x-span">
+    #[allow(non_snake_case)]
+    pub fn set__x_span(&mut self, v: longhands::_x_span::computed_value::T) {
+        self.gecko.mSpan = v.0
+    }
+
+    ${impl_simple_copy('_x_span', 'mSpan')}
+</%self:impl_trait>
+
 <%self:impl_trait style_struct_name="Effects"
                   skip_longhands="box-shadow filter">
     pub fn set_box_shadow(&mut self, v: longhands::box_shadow::computed_value::T) {

components/style/properties/longhand/table.mako.rs

@@ -9,3 +9,39 @@
 ${helpers.single_keyword("table-layout", "auto fixed",
                          gecko_ffi_name="mLayoutStrategy", animatable=False,
                          spec="https://drafts.csswg.org/css-tables/#propdef-table-layout")}
+
+<%helpers:longhand name="-x-span" products="gecko"
+                   spec="Internal-only (for `<col span>` pres attr)"
+                   animatable="False"
+                   internal="True">
+    use values::HasViewportPercentage;
+    use values::computed::ComputedValueAsSpecified;
+
+    impl ComputedValueAsSpecified for SpecifiedValue {}
+    no_viewport_percentage!(SpecifiedValue);
+    pub type SpecifiedValue = computed_value::T;
+    pub mod computed_value {
+        use std::fmt;
+        use style_traits::ToCss;
+
+        #[derive(PartialEq, Clone, Copy, Debug)]
+        #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+        pub struct T(pub i32);
+
+        impl ToCss for T {
+            fn to_css<W>(&self, _: &mut W) -> fmt::Result where W: fmt::Write {
+                Ok(())
+            }
+        }
+    }
+
+    #[inline]
+    pub fn get_initial_value() -> computed_value::T {
+        computed_value::T(1)
+    }
+
+    // never parse it, only set via presentation attribute
+    fn parse(_: &ParserContext, _: &mut Parser) -> Result<SpecifiedValue, ()> {
+        Err(())
+    }
+</%helpers:longhand>