style: Use a user defined type for font weight everywhere.

Bug: 1436048
Reviewed-by: emilio

components/style/gecko/rules.rs

@@ -25,7 +25,7 @@ impl<'a> ToNsCssValue for &'a FamilyName {
 
 impl ToNsCssValue for font_weight::T {
     fn convert(self, nscssvalue: &mut nsCSSValue) {
-        nscssvalue.set_integer(self.0 as i32)
+        nscssvalue.set_font_weight(self.0)
     }
 }
 
@@ -34,7 +34,7 @@ impl<'a> ToNsCssValue for &'a FontWeight {
         match *self {
             FontWeight::Normal => nscssvalue.set_enum(structs::NS_FONT_WEIGHT_NORMAL as i32),
             FontWeight::Bold => nscssvalue.set_enum(structs::NS_FONT_WEIGHT_BOLD as i32),
-            FontWeight::Weight(weight) => nscssvalue.set_integer(weight.0 as i32),
+            FontWeight::Weight(weight) => nscssvalue.set_font_weight(weight.0),
         }
     }
 }

components/style/gecko_bindings/sugar/ns_css_value.rs

@@ -177,6 +177,11 @@ impl nsCSSValue {
         self.set_string_from_atom_internal(s, nsCSSUnit::eCSSUnit_Local_Font);
     }
 
+    /// Set to a font weight
+    pub fn set_font_weight(&mut self, w: u16) {
+        unsafe { bindings::Gecko_CSSValue_SetFontWeight(self, w as f32) }
+    }
+
     fn set_int_internal(&mut self, value: i32, unit: nsCSSUnit) {
         unsafe { bindings::Gecko_CSSValue_SetInt(self, value, unit) }
     }

components/style/properties/gecko.mako.rs

@@ -25,6 +25,8 @@ use gecko_bindings::bindings::Gecko_CopyFontFamilyFrom;
 use gecko_bindings::bindings::Gecko_CopyImageValueFrom;
 use gecko_bindings::bindings::Gecko_CopyListStyleImageFrom;
 use gecko_bindings::bindings::Gecko_EnsureImageLayersLength;
+use gecko_bindings::bindings::Gecko_FontWeight_SetFloat;
+use gecko_bindings::bindings::Gecko_FontWeight_ToFloat;
 use gecko_bindings::bindings::Gecko_SetCursorArrayLength;
 use gecko_bindings::bindings::Gecko_SetCursorImageValue;
 use gecko_bindings::bindings::Gecko_StyleTransition_SetUnsupportedProperty;
@@ -2599,13 +2601,15 @@ fn static_assert() {
     }
 
     pub fn set_font_weight(&mut self, v: longhands::font_weight::computed_value::T) {
-        self.gecko.mFont.weight = v.0;
+        unsafe { Gecko_FontWeight_SetFloat(&mut self.gecko.mFont.weight, v.0 as f32) };
     }
     ${impl_simple_copy('font_weight', 'mFont.weight')}
 
     pub fn clone_font_weight(&self) -> longhands::font_weight::computed_value::T {
-        debug_assert!(self.gecko.mFont.weight <= ::std::u16::MAX);
-        longhands::font_weight::computed_value::T(self.gecko.mFont.weight)
+        let weight: f32 = unsafe { Gecko_FontWeight_ToFloat(self.gecko.mFont.weight) };
+        debug_assert!(weight >= 0.0 &&
+                      weight <= ::std::u16::MAX as f32);
+        longhands::font_weight::computed_value::T(weight as u16)
     }
 
     ${impl_simple_type_with_conversion("font_synthesis", "mFont.synthesis")}

components/style/values/computed/font.rs

@@ -75,10 +75,12 @@ impl FontWeight {
     }
 
     /// Convert from an Gecko weight
-    pub fn from_gecko_weight(weight: u16) -> Self {
+    #[cfg(feature = "gecko")]
+    pub fn from_gecko_weight(weight: structs::FontWeight) -> Self {
         // we allow a wider range of weights than is parseable
         // because system fonts may provide custom values
-        FontWeight(weight)
+        let weight = unsafe { bindings::Gecko_FontWeight_ToFloat(weight) };
+        FontWeight(weight as u16)
     }
 
     /// Weither this weight is bold