code: @Override
      public boolean isRunning() {
          for (Node node : mNodes) {
              if (node.animation.isRunning()) {
                  return true;
              }
          }
          return false;
      }
docs: Returns true if any of the child animations of this AnimatorSet have been started and have
  not yet ended.
  @return Whether this AnimatorSet has been started and has not yet ended.