style: Use alias for StyleAppearance.

So we could avoid generating it in rust-bindgen and drop transmute.

Differential Revision: https://phabricator.services.mozilla.com/D10304

components/style/properties/gecko.mako.rs

@@ -368,34 +368,6 @@ def set_gecko_property(ffi_name, expr):
     return "self.gecko.%s = %s;" % (ffi_name, expr)
 %>
 
-<%def name="impl_cbindgen_keyword(ident, gecko_ffi_name)">
-    #[allow(non_snake_case)]
-    #[inline]
-    pub fn set_${ident}(&mut self, v: longhands::${ident}::computed_value::T) {
-        // unsafe: cbindgen ensures the representations match.
-        ${set_gecko_property(gecko_ffi_name, "unsafe { transmute(v) }")}
-    }
-
-    #[allow(non_snake_case)]
-    #[inline]
-    pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
-        // unsafe: cbindgen ensures the representations match.
-        unsafe { transmute(${get_gecko_property(gecko_ffi_name)}) }
-    }
-
-    #[allow(non_snake_case)]
-    #[inline]
-    pub fn copy_${ident}_from(&mut self, other: &Self) {
-        self.gecko.${gecko_ffi_name} = other.gecko.${gecko_ffi_name};
-    }
-
-    #[allow(non_snake_case)]
-    #[inline]
-    pub fn reset_${ident}(&mut self, other: &Self) {
-        self.copy_${ident}_from(other)
-    }
-</%def>
-
 <%def name="impl_keyword_setter(ident, gecko_ffi_name, keyword, cast_type='u8', on_set=None)">
     #[allow(non_snake_case)]
     pub fn set_${ident}(&mut self, v: longhands::${ident}::computed_value::T) {
@@ -3091,7 +3063,7 @@ fn static_assert() {
         unsafe { transmute(self.gecko.mDisplay) }
     }
 
-    ${impl_cbindgen_keyword('_moz_appearance', 'mAppearance')}
+    ${impl_simple('_moz_appearance', 'mAppearance')}
 
     <% float_keyword = Keyword("float", "Left Right None", gecko_enum_prefix="StyleFloat") %>
     ${impl_keyword('float', 'mFloat', float_keyword)}