code: protected void setResponsiveImageSource(HtmlElement<?> mediaElement, JSONArray responsiveImageSources, Media media) {
      mediaElement.setData(PROP_RESPONSIVE_SOURCES, responsiveImageSources.toString());
    }
docs: Set attribute on media element for responsive image sources
  @param mediaElement Media element
  @param responsiveImageSources Responsive image sources JSON metadata
  @param media Media