function filterButtons(buttons, excludeClasses) {
    return shaka.util.Iterables.filter(buttons,
        (node) => {
          const button = shaka.util.Dom.asHTMLElement(node);
          for (const excludeClass of excludeClasses) {
            if (button.classList.contains(excludeClass)) {
              return false;
            }
          }
          return true;
        });
  }
Filter out buttons with given classes.

@param {!NodeList} buttons
@param {!Array<string>} excludeClasses
@return {!Array<!HTMLElement>}