Auto merge of #18066 - dadaa:make-moz-appearance-animatable, r=hiro

Make -moz-appearance animatable

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- [X] There are tests for these changes. The test code is patch part 2 in https://bugzilla.mozilla.org/show_bug.cgi?id=1382138

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components/style/properties/gecko.mako.rs

@@ -456,7 +456,10 @@ def set_gecko_property(ffi_name, expr):
 </%def>
 
 <%def name="impl_keyword_clone(ident, gecko_ffi_name, keyword, cast_type='u8')">
-    #[allow(non_snake_case)]
+    // FIXME: We introduced non_upper_case_globals for -moz-appearance only
+    //        since the prefix of Gecko value starts with ThemeWidgetType_NS_THEME.
+    //        We should remove this after fix bug 1371809.
+    #[allow(non_snake_case, non_upper_case_globals)]
     pub fn clone_${ident}(&self) -> longhands::${ident}::computed_value::T {
         use properties::longhands::${ident}::computed_value::T as Keyword;
         // FIXME(bholley): Align binary representations and ditch |match| for cast + static_asserts

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

@@ -1823,7 +1823,7 @@ ${helpers.single_keyword("-moz-appearance",
                          gecko_constant_prefix="ThemeWidgetType_NS_THEME",
                          products="gecko",
                          spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-appearance)",
-                         animation_value_type="none")}
+                         animation_value_type="discrete")}
 
 ${helpers.predefined_type("-moz-binding", "UrlOrNone", "Either::Second(None_)",
                           products="gecko",