style: Add internal overflow-clip-box-block/-inline properties and make overflow-clip-box a shorthand.

Bug: 1422839
Reviewed-by: emilio

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

@@ -373,9 +373,18 @@ ${helpers.single_keyword("-servo-overflow-clip-box", "padding-box content-box",
     spec="Internal, not web-exposed, \
           may be standardized in the future (https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box)")}
 
-${helpers.single_keyword("overflow-clip-box", "padding-box content-box",
+${helpers.single_keyword("overflow-clip-box-block", "padding-box content-box",
     products="gecko", animation_value_type="discrete", enabled_in="ua",
     gecko_pref="layout.css.overflow-clip-box.enabled",
+    gecko_constant_prefix="NS_STYLE_OVERFLOW_CLIP_BOX",
+    flags="APPLIES_TO_PLACEHOLDER",
+    spec="Internal, not web-exposed, \
+          may be standardized in the future (https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box)")}
+
+${helpers.single_keyword("overflow-clip-box-inline", "padding-box content-box",
+    products="gecko", animation_value_type="discrete", enabled_in="ua",
+    gecko_pref="layout.css.overflow-clip-box.enabled",
+    gecko_constant_prefix="NS_STYLE_OVERFLOW_CLIP_BOX",
     flags="APPLIES_TO_PLACEHOLDER",
     spec="Internal, not web-exposed, \
           may be standardized in the future (https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box)")}

components/style/properties/shorthand/box.mako.rs

@@ -58,6 +58,48 @@
     }
 </%helpers:shorthand>
 
+<%helpers:shorthand name="overflow-clip-box" sub_properties="overflow-clip-box-block overflow-clip-box-inline"
+                    enabled_in="ua" gecko_pref="layout.css.overflow-clip-box.enabled"
+                    spec="Internal, not web-exposed, may be standardized in the future (https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box)"
+                    products="gecko">
+  use properties::longhands::{overflow_clip_box_block, overflow_clip_box_inline};
+
+  pub fn to_inline_value(block_value: overflow_clip_box_block::SpecifiedValue)
+                         -> overflow_clip_box_inline::SpecifiedValue {
+      match block_value {
+          overflow_clip_box_block::SpecifiedValue::padding_box =>
+              overflow_clip_box_inline::SpecifiedValue::padding_box,
+          overflow_clip_box_block::SpecifiedValue::content_box =>
+              overflow_clip_box_inline::SpecifiedValue::content_box
+      }
+  }
+
+  pub fn parse_value<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>)
+                             -> Result<Longhands, ParseError<'i>> {
+      let block_value = overflow_clip_box_block::parse(context, input)?;
+      let inline_value = input.try(|input| overflow_clip_box_inline::parse(context, input)).unwrap_or(
+          to_inline_value(block_value));
+
+      Ok(expanded! {
+        overflow_clip_box_block: block_value,
+        overflow_clip_box_inline: inline_value,
+      })
+  }
+
+  impl<'a> ToCss for LonghandsToSerialize<'a>  {
+      fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+          if to_inline_value(*self.overflow_clip_box_block) == *self.overflow_clip_box_inline {
+            self.overflow_clip_box_block.to_css(dest)
+          } else {
+            self.overflow_clip_box_block.to_css(dest)?;
+            dest.write_str(" ")?;
+            self.overflow_clip_box_inline.to_css(dest)
+          }
+      }
+  }
+
+</%helpers:shorthand>
+
 macro_rules! try_parse_one {
     ($input: expr, $var: ident, $prop_module: ident) => {
         if $var.is_none() {