Auto merge of #17343 - ferjm:bug1355368.fontweight.keyword, r=upsuper

stylo: make font-weight descriptor in @font-face preserve keyword values

- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix https://bugzilla.mozilla.org/show_bug.cgi?id=1355368

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17343)
<!-- Reviewable:end -->

components/style/gecko/rules.rs

@@ -9,7 +9,7 @@ use computed_values::{font_feature_settings, font_stretch, font_style, font_weig
 use computed_values::font_family::FamilyName;
 use counter_style;
 use cssparser::UnicodeRange;
-use font_face::{FontFaceRuleData, Source, FontDisplay};
+use font_face::{FontFaceRuleData, Source, FontDisplay, FontWeight};
 use gecko_bindings::bindings;
 use gecko_bindings::structs::{self, nsCSSFontFaceRule, nsCSSValue};
 use gecko_bindings::structs::{nsCSSCounterDesc, nsCSSCounterStyleRule};
@@ -34,6 +34,18 @@ impl ToNsCssValue for font_weight::T {
     }
 }
 
+impl ToNsCssValue for FontWeight {
+    fn convert(self, nscssvalue: &mut nsCSSValue) {
+        match self {
+            FontWeight::Normal =>
+                nscssvalue.set_enum(structs::NS_STYLE_FONT_WEIGHT_NORMAL as i32),
+            FontWeight::Bold =>
+                nscssvalue.set_enum(structs::NS_STYLE_FONT_WEIGHT_BOLD as i32),
+            FontWeight::Weight(weight) => nscssvalue.set_integer(weight as i32),
+        }
+    }
+}
+
 impl ToNsCssValue for font_feature_settings::T {
     fn convert(self, nscssvalue: &mut nsCSSValue) {
         match self {