code: private ProgressButton addProgressButton(LinearLayout container) {
      final LinearLayout.LayoutParams layoutParams =
          new LinearLayout.LayoutParams(0, LinearLayout.LayoutParams.WRAP_CONTENT, 1.0f);
      final ProgressButton progressButton = new ProgressButton(this);
      progressButton.setLayoutParams(layoutParams);
      container.addView(progressButton);
      return progressButton;
    }
docs: Helper function that creates a new progress button, adds it to the given layout.
  Returns a reference to the progress button for customization.