mark test as not failing on mac

layout/reftests/native-theme/reftest.list

@@ -27,6 +27,5 @@
 == checkbox-still-native-when-styled.html checkbox-still-native-when-styled-ref.html
 == native-theme-disabled-cascade-levels.html native-theme-disabled-cascade-levels-ref.html
 
-# mac ignores padding on most native widgets and has done so for a while
-fails-if(MOZ_WIDGET_TOOLKIT=="cocoa") != 427122-1.html 427122-1-ref.html
+!= 427122-1.html 427122-1-ref.html