preserve whether an object property is quoted in mozilla-ast.js

lib/mozilla-ast.js

@@ -137,7 +137,12 @@
                 end        : my_end_token(M),
                 properties : M.properties.map(function(prop) {
                     prop.type = "Property";
-                    return from_moz(prop)
+                    var ret = from_moz(prop);
+                    if (prop.key.type === "Literal" &&
+                        (prop.key.raw[0] === '"' || prop.key.raw[0] === "'")) {
+                        ret.quote = true;
+                    }
+                    return ret;
                 })
             });
         },