We have a circular dependency in the build at present where webkit contains JSObject, and javafx-ui-common requires JSObject to build, but webkit requires javafx-ui-common to build. By moving JSObject to javafx-ui-common, we can break this dependency. In the future we'd like to move this to common code in the JDK so we can have a single JSObject instance also shared with nashorn, but until then, this should be in "graphics" module since it is required there.