code: public Snackbar actionLabel(CharSequence actionButtonLabel) {
          mActionLabel = actionButtonLabel;
          if (snackbarAction != null) {
              snackbarAction.setText(mActionLabel);
          }
          return this;
      }
docs: Sets the action label to be displayed, if any. Note that if this is not set, the action
  button will not be displayed
  
  @param actionButtonLabel
  @return