Remove/don’t call no-op compute_font_hash method for stylo.

This removes a potentially-costly Arc::mut call.

components/style/properties/gecko.mako.rs

@@ -1247,9 +1247,6 @@ fn static_assert() {
         unsafe { transmute(self.gecko.mFont.weight) }
     }
 
-    // This is used for PartialEq, which we don't implement for gecko style structs.
-    pub fn compute_font_hash(&mut self) {}
-
     pub fn set_font_synthesis(&mut self, v: longhands::font_synthesis::computed_value::T) {
         use gecko_bindings::structs::{NS_FONT_SYNTHESIS_WEIGHT, NS_FONT_SYNTHESIS_STYLE};
 

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

@@ -6,8 +6,7 @@
 <% from data import Method %>
 
 <% data.new_style_struct("Font",
-                         inherited=True,
-                         additional_methods=[Method("compute_font_hash", is_mut=True)]) %>
+                         inherited=True) %>
 <%helpers:longhand name="font-family" animatable="False" need_index="True"
                    spec="https://drafts.csswg.org/css-fonts/#propdef-font-family">
     use self::computed_value::{FontFamily, FamilyName};

components/style/properties/properties.mako.rs

@@ -2044,12 +2044,14 @@ pub fn apply_declarations<'a, F, I>(viewport_size: Size2D<Au>,
         style.set_root_font_size(s);
     }
 
-    if seen.contains(LonghandId::FontStyle) ||
-       seen.contains(LonghandId::FontWeight) ||
-       seen.contains(LonghandId::FontStretch) ||
-       seen.contains(LonghandId::FontFamily) {
-        style.mutate_font().compute_font_hash();
-    }
+    % if product == "servo":
+        if seen.contains(LonghandId::FontStyle) ||
+           seen.contains(LonghandId::FontWeight) ||
+           seen.contains(LonghandId::FontStretch) ||
+           seen.contains(LonghandId::FontFamily) {
+            style.mutate_font().compute_font_hash();
+        }
+    % endif
 
     style
 }