addButton(name, onclick, yesNoDialogText) {
    const button =
      /** @type {!HTMLButtonElement} */(document.createElement('button'));
    button.classList.add('mdl-button');
    button.classList.add('mdl-button--colored');
    button.classList.add('mdl-js-button');
    button.classList.add('mdl-js-ripple-effect');
    button.textContent = name || '';
    button.addEventListener('click', () => {
      if (!button.hasAttribute('disabled')) {
        if (yesNoDialogText) {
          this.makeYesNoDialogue_(this.actions_, yesNoDialogText, onclick);
        } else {
          onclick();
        }
      }
    });
    this.actions_.appendChild(button);
    return button;
  }
Adds a button to the bottom of the card that will call |onClick| when
clicked. For example, a play or delete button.
@param {?string} name
@param {function()} onclick
@param {string=} yesNoDialogText
@return {!HTMLButtonElement}